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Growth of follicles in the ovaries of the bat myotis lucifugus lucifugus.

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FIVE FIGURES
IPITTRODITCTION
The cliaiiger Tvliich talic placc~in the o v a r i f l h during the
rcproductire. c-j-clc have bccii studied cxte.imiwly in mammals,
such as the. rat and mouse, which liaw i*clatirrlysliort oestrous
cycles. Evans and S ~ v e z y ( '31) have. rccordcd that during
each cycle a coiisidemhle gronp of follicles hegins growth.
Some oS tliese complcte their clift'ercii tiation sncl rnpt1ii.e ; the
majority undergo retrogressiou. h the m o u e it secms c+ar
that this periodic iiiitiatioii of activity ill tlir germ wlls inrolves thc germirial cpitlicliiim ( L1llen, '23 ; Allen aiitl Cwaclick, ' 3 7 ) .
hi the bats of thu temperate zone t h c w is only one rcyroductive cycle each year. T ~ species
P
M yol is lucifugus lucifngus, which is il cave residont in Missouri (luring thc wiiitct(Gnthrici, '33 a ) , €allows the general p a t t t ~ nf o r such rriariimals. OvuIatioii is spoiitancwis a n d o c ~ u r somctirne
s
in April,
w h e n ~ v e iilici
~ feniales l e a w ttic (*ares. A siiigle tei-tiarv, or
\~esicida~
follicle
~,
cwiitaiiiing a small antrum is Pwsciiit i r i October at t h e onsrt of the (?aw-duelJing period a n d grows but
littlcl, if at all, until the prrovulation pe.rioc1 i i t ilir spring.
Primary folljcles, consisting of a sirigle layer of squamous
cells, arid both niiilaminar. a r i d multilaminar srcoiidary 01'
growing follicles are conspjcnoiis t Iiroughout thc so-ca1lcc.l
* 'rhe multilaminar srcondary follii-les corrcrpond to folliclc typrs 2 to 5 (I!.
qcribetl b.r I'iiicus : ~ n dE1i7rriaiin ( ' 3 7 ) for the r:~bkiit. 'r1it.y do iiot rceognize the
uni1artiin:rr serondarp folhcle, in nhicli t h e s q i i a m o ~ i scells of the primarp follicle
lrarr 'x)rcoinr cuboidal, a s ii t j p ~ .
47'7
hibernating mouths. Insemiriation occur-s in tho autumn, but
ferriales appareiitly again hecomr rcwplive to males iu ~ ) e r i o d s
of activity as the u-iiiter advaxiccls. Sperm arc phagoc~-tizcti
iii the uterus and eliminated tlirougli the vagiiia (luring the
winter (Gutlii*ic, '33 1 1 ) . The prwcnccl of the vesicular follicle
aiid the evidence of ~ ~ ~ u r r ciiisemiiiationr
iit
before its rupture
made it seem lilic~lythat these aiiimals were in coiitiiiuons
oestixs from Octoher t o April (compare ('afier, '34; M K e 1 aucl Kolbow, '34). Granliiig this possibility, xvhat woiilcl be
the effect up011 tlie gimvth of mx)iiilar-y follicles ? TTould a
ln?o~i~leclge
of the total follicle popillation he of valur in clarifying our untlc*rstan(liiig of tlie i*ept-oductivccycle ?
I n order to aiis\ser tliese questions a c'eiisu5 of all normal
gro\viiig follicles a r i d follicles in carlv stages of retnogrcssion
was made in lioth ovaries of a series of females in which a
c y t o l o g i d study of the ovaries had bceii made (Guthi-ie arid
*Jeffers, '38 a ) . ('omparable oll?sers.ations have bee11 made 011
ovaries of Al . jii*iwsc~ns
collected at intervals thro1igliout the
Tear arid will be prescnlecl elsewhcrc.
G R O W T H O F FOLLICLES IN T H E BAT
479
a solution of 3% potassium bichromate f o r 1 day each. Dehydration and embedding in parafin wcrc carried out in the
usual way, using xylol as a clearing agent, and serial sections
were cut at 3 or 4 p . Sections were stained bv Kull's acid
fuchsin-thionin-aurantia method (Lee, '37, p. 306).
The smallest follicles included in the counts consisted of a
single layer of cuboidal cells around an oocyte, that is, they
mere unilaminar secondary or growing follicles. Primary follicles were not considered. Two diametcrs of cach follicle
were measured and the average taken as the diameter of the
structure ; the theca was not included. Measurements were
made at a magnification of x 600 with an ocular micrometer,
each unit of which was equal to 4 p at this magnification.
OBSERVATIONS
Normal follicles
The number of normal growing follicles in both ovaries of
this bat varies in different individuals from 53 to 305, exclusive of the singlc vesicular follicle (table 1). The average
number of follicles is 157. I n 22.2% of the bats studied, less
than 100 follicles are present; in 46.7%, between 100 and 200
follicles occur; and in 31.1%, over 200 follicles arc found. I n
only one individual (2.2%) are thcre more tlian 300 follicles.
To find the relationship between the age of bats and the
number of follicles in their ovaries, the forty-five animals were
divided into groups on the basis of the amount of wear on
their teeth. I n the group of the youngest bats, with no wear
on the teeth (twenty individuals), the number of follicles
varies from 53 t o 305 (average 182.3) ; in bats showing some
wear on the teeth (elcven individuals), the variation is from
87 t o 284 (average 168.7) ; and in the fourteen bats in which
the teeth are conspicuously worn, from 65 to 173 follicles
occur (average 110.1).
In order to detcrrnine wheiher there is a preponderance of
follicles in a single ovary of the bat, the percentages of the
total normal follicles occurring in the right ovary and in the
THE ANATOMICAL RECORD, VOL.
71. N O 4
TABLE 1
Counts of follicles in individual bats
1
I
SERIAL
DATE O B
S O . OF
cnI,mc-
BAT
TION
XVXBER OF FOLLICLES
.
..._..
+
DIAMETER
.-ca
E
2
4
!4
~~
164 to 1 8 3 /r
598
614
1128
640
13 31
639
1129
1085
668
672
687
689
710
734
736
1157
738
1159
1165
1170
756
1090
1089
1092
776
778
1183
1176
1175
830
1095
1100
1192
1199
1191
1193
1209
1214
1210
956
954
1224
1225
947
1024
10-19-31
10-28-31
10-31-34
11- 8-31
11- 9-34
11- 8-31
11- 9-34
11-10-33
11-21-31
11-21-31
12- 3-31
12- 3-31
12-12-31
12-26-31
12-26-31
12-27-32
12-2&31
12-27-34
1-14-35
1-14-35
1-16-32
1-22-34
1-22-34
1-22-34
2- 6-33
9- 6-32
2-21-35
2-21-35
2-21-35
2-20-32
3-10-34
3-10-34
3-14-35
3-14-35
3-14-35
3-14-35
3-2 9-3 5
3-29-35
3-29-35
4-16-32
4-16-32
4-22-35
4-22-35
4- 2-32
4- 6-33
68
85
80
28
103
96
130
178
31
54
54
43
67
43
121
86
167
183
116
133
55
194
86
154
114
82
78
88
103
53
169
145
97
114
56
43
76
112
71
113
157
197
74
128
52
31
57
47
21
83
61
95
I)
4
2
1
2
94
16
45
19
20
50
29
54
41
49
45
27
58
28
84
26
64
66
57
44
34
63
18
91
57
32
39
21
16
48
47
29
25
72
83
49
61
21
-
5
1
2
14
4
28
16
17
15
10
9
11
2
11
in
1
1
1
1
5
16
2
8
6
4
1
5
5
2
8
8
2
~
1
28
7
16
10
1
1G
8
27
11
14
8
23
4
7
14
1
8
8
28
3
9
5
2
1
15
12
4
5
15
14
-
a
26
8
1
4
30
16
33
22
5
22
9
ti
20
5
11
7
12
8
13
G
14
14
6
12
4
17
7
10
8
16
22
21
6
11
14
9
10
17
9
5
8
56
31
10
3
-
2
2
1
2
2
1
~
108
144
141
.
3i
214
173
242
287
57
108
84
63
128
82
203
134
232
238
144
207
92
305
123
222
188
162
126
128
170
72
268
210
129
181
81
68
129
161
101
173
241
284
128
204
87
2
30
9
6
31
16
35
22
5
27
9
9
20
5
13
7
13
9
13
6
1(i
14
6
15
6
18
12
10
8
31
24
29
12
15
16
14
15
19
9
5
16
64
33
10
4
-
345
358
305
3,54
418
359
348
371
376
2 80
308
279
322
373
388
350
368
394
273
359
318
400
382
3 74
342
382
328
422
388
402
384
324
337
417
x
3.53
345
388
318
484
326
375
361
c.1.
c.1.
EXPLANATION:
Animals are arranged chronologically in the order in which they are plotted
iu figure 3. A space separates the groups collected at comparable dates. c.l., corpus luteum;
*, vesicular follicle damaged.
480
G R O W T H O F FOLLlCLES I N THE EAT
481
ovary coiitaiiiiiig the vesiculai. follicle were calculated for each
individual. I n 49% of tlie bats tlie vesicular follicle is in the
right ovary.2 The data on the number of follicles in a single
ovary have been plotted (fig. l), and it is seen from the graph
that the follicles are not constantly more numerous in one
ovary than in the other. The curves s h o ~ vthat in a single
animal as little as 39.6% or as much as 60.4% of the total follicular population may he present in oiie ovary. HoweT-er, if
Fig. 1 Graph showing the percentage of normal growing follielcs present iu
the right w a r y and in the ovary containing the single vesicular follicle in individual bats.
the figures for the forty-five animals are combined, it is found
that 49.5% of tlie total number of follicles in these animals is
in the ovary with the vesicular follicle, while 50.8% is in the
right ovary. In neither case is the deviation from a 1:1ratio
of statistical sigiiificaiice.
Tlie bats were grouped together on tlie basis of the dates
on which they were collected, and the average number of total
2While the vesicular follicle occurs a s oftcn in the left ovary as in the right,
implantation in hundreds of hfyotis observed is always in the riglit horn of the
uterus. After the feniales reach seuual inaturitv the right horn is larger than
the left throughout the year.
482
M. J. GUTIll1IE AKD K. R. JEFFEEIS
normal follicles calculated for each date. Figure 2 shows that
the average number varies throughout the minter and spring
months. The curvc reaches peaks in early November, in late
December and January, and again in late March and April.
This curve is in many respects similar t o that of the distribution of the smallest follicles measured (compare fig. 4).
Fig. 2 Graph showing average numbers of all normal growing follicles and of
follicles in early stages of retrogression in bats grouped in accordance with the
dates of collection.
The normal secondary follicles in the ovaries of M. lucifugus
lucifugus range in size from 24 to 1 5 7 p in diameter. These
follicles were classified in four groups on the basis of size.
The percentage of the total follicular population found in each
group mas calculated for each individual and the results
plotted (fig. 3 ) . The marked individual variation in the distribution of follicles of different sizes is shown by the graph.
The combined data for individuals killed at comparable
dates are shown graphically in figure 4. The curve for fol-
483
G R O W T H O F FOLLICLES I N T H E BAT
size groups in individual bats arranged in accordance with the dates Of collection.
%
.
10
i-Lu
3- 5 4
- 3
2
I-
m
m
5%
s 3
:5
J,
e - 0
3-$srJ
g.2
0
U- 3
Fig.4 Graph showing percentage of normal growing follicles in the different
size ranges in bats grouped in accordance with the dates of collection.
THE ANATOXICAL RECORD, VCI,.
71, NO. 4
484
M. J. GUTHRIE AND K . R. JEFPEXS
licles 24 to 43 in diameter shows that there are periodic
variations in the relative numbers of these follicles. They are
very numerous toward the end of October, during late December and throughout January, and, again, during the last of
February and most of hlarch and Spril. I n the two animals
in which ovulation had occurrcd, thcre is a dccrease in the
number of these small follicles. The curve for follicles 44 to
83 11 in diameter also shows periodic variations. It has a conspicuous peak in early December, which we interpret as being
conditioned by the peak in the curve of follicles 24 to 43 p in
diameter seen in late October. There is another rise in the
curve in Fehruary, following the December and January increase in the smaller follicles. The remainder of the curve is
without conspicuous variation. The curve f o r folliclcs 84 to
123 p in diameter reveals two marked rises in the relative
numbers of these follicles; the first occurs toward the end of
November, the second is a t its height early in February and
follows the December peak in the curve for follicles 44 to 83
in diameter. The curve f o r the largest normal secondary
follicles, 124 to 163 p in diameter, indicates no marked variation in the relative numbers of these follicles, although the
slight rise in Deeembcr, following the November increase in
follicles 84 t o 124 p in diame
may be significant.
The diameter of the vesicular follicle varies during the winter months from 273 to 422 p (table 1). The largest follicle
observcd, from a bat killed April 16th (no. 956), had a diameter of 484 p and contained an oocyte with a meiotic spindle.
There is no indication that any marked growth of the tertiary
follicle occurs until the period just before ovulation. The
average diameter of seren vesicular follicles in November is
358 p and of cight similar follicles in llhrch is 358.5 p.
Retrogre.ssi.lzg follicles
Follicles a t all stages of degeneration occur in the ovaries
of M. lucifugus lucifugus during the months when collections
were made (sec Guthrie and Jeffers, '38a, for criteria of
retrogression with stages and types). Only those in early
GR OWTH O F FOLLICLES I N T H E BAT
485
stages of retrogression of type I were measured and counted ;
their diametcrs have riot yet decreased as a result of disintegration of the granulosa cells, and it is possible to determine
how large they were when retrogression began. From 2 t o 64
of these follicles are found in different individuals (table 1);
L
a
40
-
30
-
a
n
6
z
Fig. 5 Graph showing average numbers of all follicles in early stages of retrogression and of such follicles in different size ranges in bats grouped in accordance
with the dstcs of collection.
the average number for the forty-five bats studied is 15.7. In
40% of the animals, 10 o r less occur; in 37.8%, 11t.o 20 are
found; in 11.1%,there are 2 1 to 30; in 8.9%, 31 to 40 are
present; and in only one bat (2.2%), do more than 40 such
follicles occur.
486
111. J. GLTTHRTE AXD K. R. JEFFEBS
The counts of follicles in earl7 stages of retrogressioii for
bats collected on comparable dates were combined, tlie a r e r age computed, and the data plotted (fig. 2). From the graph
it is seen that, aside from the two individuals killed April 22nd
in each of which atypical persistence of the vesicular follicle
iws noted, there is no pronounced variation in the number of
degenerating follicles during the months in which collections
coulcl be made. However, slight increases in retrogression of
follicles occur early in November and about the middle of
March.
The size at which follicles begin to degenerate varies
markedly. The smallest follicles in which degenerative
changes a r e found i n the granulosa a r e 67 p in diameter, the
largest 182 p. Three-tenths per cent of the retrogressing follicles measured a r e 64 to 83 p in diameter; 55.5% a r e 84 to
123 p ; 42.77., 1 2 1 to 163 11; and 1.5%, 164 to 183 p in diameter.
If the average number of degenerating follicles of different
sizes is calculated for bats collected at comparable dates
(fig. 5) i t becomes evident that from October until the middle
of February approximately two-thirds of the follicles beginning to degenerate are 124 to 163 p i n diameter; about onethird are 84 to 123 p in diameter. A few retrogressiiig follicles
164 to 183 p in diameter ( a total of ten) a r e found during this
period. After February Gth, there is a marked increase in
the number of follicles 84 to 123 p in diameter that begin to
degenerate and a decrease in the number of retrogressing
follicles 124 to 163 p in diameter.
nrscussIoR
The number of normal follicles found in tlie ovaries of the
bat is considerahly smaller than that reported f o r the rat
(Arai, '20; Swezy, '33 a ) , the mouse and ape (Blotvogel, '32),
and the rabbit (Desaiw, ' 3 5 ) . H O W ~ V
for
C tlie
~ , niialysis presented in this paper, only the secondary growing follicles were
counted ; the primary follicles and the tertiary follicle were
not included. F o r this reason the counts gireii here a r e not
comparable with tliose of most other investigatoi*s.
Arai ('20) reported that the ratio of the number of oocytes
in the right ovary to that in the left was 1.03: 1.00; for the
cntire series of rats, 50.676 of the oocytes occurred in the right
ovary. F o r the forty-five 31. lucifngus lucifugus studied, it
was found that 50.8% of the normal growing follicles were in
the right ovary.
I n the rat, Arai ( ?20) determined by counting all the oocytea
in both ovaries of thirty-nine individuals 1 to 947 days old
that the number of oocytes decreased rapidly u p to 20 days
of age, after which the decrease was inore gradual. The
counts i n 31. lucifugus lucifugus suggest that a similar gradual
decrease i n the number of growing follicles occurs with age,
but t.he number of indkiduals in each age group is small and
the varjation in tlie number of follicles is great.
Since only the growing follicles i n the ovaries of the bat
wcre counted, the data presented can throw light only on the
growth of follicles, not on the seasonal variations in the proliferatioii of new oocptes, although differentiation of cells of
the germinal epithelium is belicved t o occur throughout adult
life (Guthric aiid Jeffers, '38 a ) . Allen ( '23) counted the
mitoses in tlie cells of the germinal epithelium of the ovaries
of mice at different stages of the oestrous cycle. A cj-die
proliferation of the cells of thc germinal epithelium, which
had its peak at ocstrus, was found. H e regarded this as the
first stage of ovogenesis. These results have becn confirmed
by Allen and Creadick ( ' 3 7 ) . Evans and Swezy ( '31) reported that the proliferation of oocptes and the growth and
degeneration of follicles were cyclic phenomena which c o n e spondccl in tlie rat, guinea pig and dog with the clianges occurring during the oestrous cycle (compare Swezy, '33 b). Whilc
new sex cells were formed at all periods of the oestrous cycle,
the proliferation of new oocytes was most marked during
metoestrus, the number of growing follicles \\-as at a maximum
during anoestrus and at a minimum during oestrus. Myers.
Young and Dempsey ('36) have reported that, in the guinea
pig, follicles began to grow a t all stages of the oestrous c p l e .
However, only those follicles heginning growth during a lim-
488
M. J. BUTHRIE AND Ei. R. JEFFERS
ited interval reached maturity and ruptured a t the following
oestrous period; all others degenerated. I n contrast t o these
findings, the connts of normal growing follicles in the ovaries
of &I. lucifugus lucifugus indicate that, instead of a single
waiTe of growth or a continuous iiiitiation of growth in primary follicles, there are at lcast four peaks of follicular
growth in this bat during the oestrous cycle. The curve for
follicles 24 to 43 p in diameter reveals thrce waves of growth
in them during the 6 months studied (fig. 4). That these three
are probably preceded by a t lcast one other growth wave is
suggested by the pronounccd rise in the curve f o r Polliclcs 84
to 123 p in diameter late in November. The peaks of the three
growth waves shown by the curve for follicles 24 t o 43 p in
diameter occur at intervals of 60 to 75 days, and the peaks in
the curves for follicles 44 to 83 and 84 to 123 p in diameter
appear at intervals of about 75 days.
It is possible, by means of the data plotted in figure 4, to
estimate the rate a t which folliclcs p o w in 31. lucifugus lucifugus during the period of so-called hibernation. The peak in
the curve of follicles 24 to 43 p in diameter for October 28th
is followed in 45 days by a peak in the curve for follicles 44 to
83 p in diameter, Similarly, about 43 days after the December
and January increase in the number of follicles 24 to 43 p in
diameter there is an increase in the number of follicles 44 to
83 p in diameter. A comparison of the curve f o r follicles 44
to 83 p in diameter with that for follicles 84 to 123 p in diameter shows that there is an interval of a little over 60 days
between the corresponding peaks in the two curves. It requires, therefore, approximately 105 days for follicles 24 to
43 p in diameter to become 84 t o 123 p in diameter, which is
near the limit of size attained by follicles before they begin
to degenerate.
No conspicuous wave-like variations in the numbers of degenerating follicles have been found to occur in the bat between Octoher and the middle of April. However, it is interesting to note that there is a marked change beginning in
February in the size attained by the secondary follicles before
GROWTH O F FOLLICLES IN TIIE BAT
489
they begin to degenerate. During the months from October
to the middle of February, follicles may become relatively
quite large before they degenerate ; two-thirds of the retrogressing follicles are over 124 p in diameter. S f t e r the middle
of February, the majority of the degenerating follicles are
smaller than 124 [I in diameter. It appears that something is
limiting the growth of follicles beyond a certain size but not
increasing the number of retrogressing follicles.
The reproductive cycle of the bat is known to have many
peculiarities. First to be recognized were the facts of autumnal insemination and vernal ovulation. It has generally been
held that the eggs are fertilized by sperm retained in the tract
throughout hibernation (compare Hartman, '33). Observations on tho tracts of maiiy recently killed females (Guthrie,
'33 b), the behavior of artificially ovulated eggs (Guthrie and
JeEers, '38 b), and the presence of abundant sperm in males
of the species throughout the winter (Miller, '36, '37) have
convinced us that, under the climatic conditions of central
Missouri, spring copulations are the rule in these bats. Where
the winters arc more severe and temperatures more constant
it seems possible that different reactions may prevail in the
bats.
With the information accumulated over a period of years
we may now formulate a n explanation of the correlation of
certain activities related to reproduction in the female bat.
Since the cells of the pars distalis of the hypophysis of this
bat have been shown to be understandable as stages in the
differentiation of a single type of secretory cell (Guthrie,
Jeffers and Sawyer, '36; Sawyer, '36) we shall assume that
one secretion is produced by these cells. It is obvious that the
preparation of however many hppophyseal extracts producing
varied responses in several regions of the body does not establish that the active principles of such extracts exist as such
in the intact gland (cornpare van Dyke, '36, pp. 174-175). Nor
does the observation that a particular region, which is undergoing differentiation, seems to respond at one time to one
fraction and at another time to a different fraction necessarily
490
M. J. GCTHBIF, ANT) K . R. J E F P E R S
suggest more tliaii that cells are capable of diflereiit reaction*
and have different thresholds of response when in successive
stages of differentiation. The effector cells are not static : the
reaction is conditioned not only by the stimulus but by the
effector (compare Maxwell, '34 ; Engle, ' 3 2 , pp. 7%-'796 1.
Lillie and his associates 1iaT.e made use of the concept of
growth rate and hormone threshold in their brilliant analysis
of feather patterns (compare Domm, Gustavson and Juhn,
'32, pp. 636-637). Zuckerman ( ' 3 7 ) has suggested that a
variation in threshold to ocstrogcnic hormone is exhibited by
the uterine endometrium of the monkey.
When females of M. lucifugus lucifugns enter the eaves in
the autumn there is a single follicle mitli a small antrum in
the ovaries of each individual, the vaginal epithelium is cornif i ~ d and
, ~ the uterus contains sperm. These individuals are
in a state of oestrns as judged b ~ the
- criteria of vagiiial reaction and receptivity to males. However, the uteriis is not
fully differentiated nor does ovulation immediately ensue. Let
us assume that this state has been coriditioned in the following
may. During the summer, when these bats arc actirc and
feeding each night, follicles grow under the influence of the
gonadotropic hormone of the hypophysis. At least oiie of
these follicles reaches the stage of differentiation at whicli
an oestrogen is prodneed in a quantity sufficient to condition
raginal cornificatioii a i d the response to males, but not to
initiate differeritintion in tlie uterus o r tubes. These animals
appear to correspond to Pfeiffer's ( ' 3 3 ) 'single constant
oestrous' rats, except that the mating reaction has been induced. There is nothing to suggest that progestin has been
responsible f o r tlie onset of receptivity, as Young ( ' 3 i ) has
postulated f o r the guinea pig, since no luteiiiization of follicles is observed. We shall use the phrase 'submaximal oestrus'
Statements concernirig tlie condition of thc reproductile tiact are based on
unpublished obserratioiis by Elizabeth 31. Recdcr, P1i.D. thesis, Unir. of Mo., 1935.
4 W e have no evidence that more than onc tertiary follicle is produced in 11.
lucifugus lucifugus since v-e h a ~ eno specimens taken a t the season n hen aevcrd
follicles with antra are f o u n d in the ovarics of M. grisesceiis (compare Gutlirrc
and Jeffers, '38 a ) .
G R O W T H U F FOLLICLES IA- T H E BAT
499
(Witschi ailti Pfriffer, '35) to designate the coiiditioii of female bats which have entered the cams.
At the lower metabolic level of the early liibernating periocl
(November) the gonadotropic hormonal output of the liypophysis is reduced and the average number of growing follicles is lowered while retrogression is conspicuous in the
larger secondary follicles. The single tertiary follicle undergoes no detectable change, and retrogression of the secondary
follicles is not accompanied 1))- luteinization of the granulosa.
It is interesting to note that Foster, Foster and Hisaw ( ' 3 T )
report a comparable manner of retrogression of follicles in
hypoplipsectomized adult rabbits and find that small follicle^
with antra may persist and be capable of stimulation to g r o ~ v
f o r about 30 days after the removal of the gland.
By December the average number of growing follicles in
these bats is greatly reduced, and the wave of retrogression
is subsiding. One may assume that follicles growing at a
certain rate require and take available hormone in a certaiii
qimntitp. TThen the hormone has fallen below that level and
many follicles have undergoiie retrogression the net result is
a relative increase in the hormone available. The response to
this is a gradual increase in growing follicles of the smallest
size raiige. Such follicles have been stated by a nnmloer of
workers to be independent of any hypophyseal iiiffuence as a
result of studies on immature, growing animals or hypophysectoniized adults. This matter is discussed in another place
where the results of injection of hypophyseal extract upon
these smallest growing follicles are presented ((luthrie and
Jeff ers, '38 In). Foster, Foster and Hisaw ( '37) reported that
a few primordial follicles persisted in the rabbit ovary for as
long as 90 days after bypophysectomy. This observation,
together with the long survival of follicles with small antra
under the same circumstances, suggests that the total secretion of the hypophysis may not act directly on the gonad but
through an intermediary. After hypophysectomy a low level
of gonad stimulating substance from such a soiirce maintains
a limited number of follicles at certain stapes of differentia-
492
M. J. GUTEIRIE A&-D B. H. JEPFEXS
tiori f o r a considerable time. The smallest 91-owi13g follicles
are capable of respoiisc to very small quantities of this substance.
The number of smallest growing follicles in tlie bat undergoes a relative increase until about the middle of January
when there is a rise in the percentage of larger secondary
follicles ~ h i c his conspicuous early in February. This is believed to be induced by an incrcasc in the amount of gonadotropic hormoiie available, wliicli is correlated with changing
temperature conditions and a n elevation of metabolic level in
the bats as indicated by evidence of shifting populations at this
time (compare Gnthrie, '33 a ) . Along with this increase in
number of larger secondary follicles the output of the oestrogenic substance increases and the females are again receptive
to males in periods of activity. It is during this time that
spontaneous ovulation under laboratory conditions begins
(Guthrie and Jeffers, '38 b). By the end of February, however, the number of growing follicles has become too large for
tlie amount of gonadotropic hormone arailable and retro;0 ression is again on the increase, this time among smaller follicles.
T17ith the release of this drain on tlie supply of gonadotropic
hormone the smallest follicles show a relative increase.
Toward the end of Ifarch, as the time of emergence from
the caves nears, there is an increase in the average number
of growing follicles again, but the tertiary follicle shows no
definite trend toward increase in size so long as the females
remain in the caves. We have by chance obtained one individual (no. 956) in which preovulatory growth has occurred.
TTTe believe that with an increase in metabolic activity the
amount of gonadotropic hormone finally rises until the threshold of response of the tertiary follicle is reached. When this
happens the tertiary follicle undergoes very rapid growth, and
ovulation and smelling of uterus and tubes occur within 24
hours in many individuals removed from the caves at this
time of year. This hypothesis that preovulatory growth and
ovulation require a very high level of available gonadotropic
hormone is consistent with the observation that the large
G R O W T H O F FOLLICLES I N TI-IE BAT
493
graafian follicles are the first to respond t o diminution of the
hormone in the hypophysectomized rabbit (Foster, Foster and
Hisaw-, ' 3 7 ) , and that a large final intravenous injection of the
follicle stimulating or of the luteinizing fraction of hypophyseal extract appears necessary in order to induce ovulation in the anoestrous cat (Foster and Hisaw, '35). Witschi
and Yfeiffer ('35) used a large dose of the luleinizing fraction of the gonadotropic hormone in order to produce ovulation in their rats which were in submaximal oestrus.
In the bat there seems no reason t o postulate the presence
of more than one gonadotropic hormone if the possibility of
differing thresholds of response in follicles at the several
stages of differentiation be granted. There is no indication
of any lnteinixation except in the granulosa of the follicle of
oviilation. There is nothing wliich suggests to us that a swing
from F.S.H. secretion to L.H. secretion occurs under the influence of an ocstrogenic substance (compare Witschi and Pfeiffer, ' 3 5 ; Fevold, Hisaw and Breep, '36). A single gonadotropic hormone which is produced or becomes available in a
limited quantity and for which follicles compete at all stages
of growth but at different thresholds is adequate t o explain
the peculiarities and duration of the oestrous period in the
bat. Evans and Swezy ('31) found for several mammals that
the period when most follicles underwent retrogression was
when a few completed the preovulatory growth. They found,
also, that gestation did not inhibit the c j d i c growth and degeneration of follicles, even though ovulation did not occur.
Follicles growing during gestation sometimes luteinizcd in the
r a t but not in the guinea pig. Dempsey ('37) could find no
effect of oestrogenic substance (progynon B, Schcring) on
rhythmicity of ovarian response in the guinea pig. The hibernating female bat is in submaximal oestrus as a consequence
of an inadequate quantity of available gonadotropic hormone.
x.J. GUTHEIE a m
494
I<. I:. JEYFERS
SUMMARY
1. The nuinber of normal growing follicles in the ovaries of
11.lucifugus lucifugus ranges from 53 to 305 ; the average is
157 follicles, sdiich are cqually clistributed in the two ovaries.
The average iiiimber of normal growing follicles decreases
somewhat with age.
2. The periodic variations in the relative iiumbers of follicles of clifferent sizes which occur in the ovary during the
months from October through April are interpreted as indicating follicular growth waves. Three peaks of growth are
evident in follicles 24 to 43 p in diameter, and these are followed by peaks of growth in the larger follicles. A fourth
growth waw just prior to hibernation is suggested by the data.
3. Follicles in which retrogression is beginning vary in number from 2 to 64 in different individuals ; the average is 15.7.
From October until the middle of February, approximately
two-thirds of the degenerating follicles are 124 to 183 p in
diameter; from February 21st on, the majority of the retrogrcssing follicles are 64 to 123 p in diametei-.
4. The four growth waves of the secondary Iollicles occur
during a. single ocstrous cycle which terminates at the time of
rupture of the one vesicular follicle present throughout the
so-called hibernating season.
5. Tlie hibernating female bat is in a state of submaximal
oestrns conditioned by an inadequate quantity of a single
gonadotropic substance.
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ARAI, H. 1920 0 1 1 the postnatal dcvelopment of the ovary (albino r a t ) , ~ i t h
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GROWTH OF FOTJJCT,ES Ihi T H E RAT
493
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