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On the relations between the mesenchy-mal spaces and the development of the posterior lymph hearts of turtles.

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From the Laboratories of Animal Biology, State University of Iowa
In a recent paper read before the American Society of Zoologists,
Central Section, the writer called attention to the fact that, in
the turtles, the mesenchymal spaces play a much more important
part in the development of the lymphatic system than they seem
to play in mammals. In a later paper before the Iowa Academy
of Science, on the “Development of the Posterior Lymph Hearts
of the Loggerhead Turtle,” considerable stress was placed upon
the importance of the intercellular lymph spaces in initiating the
development of the lymph hearts. Since then a more careful
study has been carried on with special reference t o these spacesin
embryos just before, at the time of, and immediately after the
first appearance of the anlagen of the posterior lymph hearts.
It is the purpose of this paper to consider merely a few of the results
obtained by this study. A more detailed account is reserved for a
later paper on the anatomy and development of the entire lymphatic system of the loggerhead turtle.
The embryonic material forming the basis for this work was
collected by the writer at the Marine Laboratory of the Carnegie
Institution at the Dry Tortugas, Florida. I wish here to express
my deep obligations to Dr. Alfred G. Mayer, Director of the Torh g a s Station, for valuable assistance in collecting the material ;
and to Professor Gilbert L. Houser for many helpful suggestions
during the pursuance of this investigation.
A great deal of attention has’been paid to the methods of preparing the materials for study during this research. It is extremely
important for the correct interpretation of the significance of the
mesenchymal spaces that the tissues of the embryo should be preserved in as nearly their natural condition as possible. A full
account of the methods Will be given in the later paper.
The posterior lymph hearts of turtles are a pair of elliptical,
pulsating organs situated immediately below the carapace, just
back of the upper ends of the iliac bones, one on each side of the
body. They drain the lymph cavities and lymph channels of
the posterior extremities and pelvic regions, and open into tributaries of the posterior renal advehent veins.
The only important work that has hitherto been done in the
development of the sauropsidian lymph hearts, as far as is known
t o the writer, is that on the chick by Sala (’00). According t o
Sala’s researches, the posterior lymph hearts are derived from the
first five coccygeal veins of each side by a process of dilation and
confluence. He finds that small spaces or fissures develop in direct
connection with the lateral branches of these veins. These fissures
appear to be merely the simple dilation and ramifications of the
veins themselves. These spaces or fissures enlarge and fuse with
each other, producing a “system of cavities, very irregular in form
and dimensions, intercommunicating, and connected at the same
time with the lateral branches to the first five coccygeal veins.”
The cavities subsequently fuse to form a single cavity for each
lymph heart.’
The posterior lymph hearts of the turtles are closely related in
their development to the formation of a pair of vessels, extending
along the outer surface of the muscle plates of the post-iliac regions,
and forming one of the main tributaries of the renal portal system
of each side. This pair of veins we shall designate in this paper as
the right and left caudal branches of the posterior renal advehent
veins. They correspond to the venae ischiadicae of many authors.
The right and left caudal branches of the renal advehent system
1 Sala; “ Sviluppo dei Cuori Linfatici e dei Dotti Toracici nell ’Embrionedi Pollo,”
pages 269 and 270. See, also, Huntington; Anatomical Record, vol. 2, p. 34.
arise by the longitudinal anastomosis of the dorsolateral branches
of the postcardinal veins, posterior to the opening of the iliac
veins, and just outside of the muscle plates. They continue backward into the tail as the lateral coccygeal veins, and forward as the
main branches of the advehent system of the Wolffian bodies.
The development of the lymph hearts is directly related to that
portion of these veins formed by the first two or three post-iliac
branches of the postcardinal veins.
The development of the posterior lymph hearts is initiated in the
loggerhead turtle by the vacuolation of the subcutaneous mesenchymal tissue of the post-iliac regions. As early as the middle of
the second week of development, a noticeable change in the mesenchymal cells of this region is clearly seen. The mesenchyme becomes very loose and spongy. Toward the close of the second
week, the mesenchymal spaces enlarge and fuse with each other.
There is thus formed a network of intercommunicating spaces
which invest and communicate with invading capillaries from the
first two or three post-iliac branches of the postcardinals. Fig. 1
is a camera lucida drawing of a small portion of this area under the
homogenous immersion lens. The spongy appearance is not
sufficiently brought out in this drawing,yet it shows to some extent
the nature of the vacuolation, and the relations of the spaces
to the blood capillaries. By the middle of the third week of development, the dorsolateral branches of the postcardinal veins have
fused at their distal ends to form the caudal branches of therenal
advehent system. The formation of this pair of veins produces
profound changes in the post-iliac spongy area. Great spaces or
channels appear. These spaces seem to be enormously dilated
capillaries which intercommunicate with each other, and connect
with the accompanying veins at one or two points. They contain
red blood cells, and are indistinguishable from the veins of that
region, except by their position. They correspond to the venolymphatics of birds and mammals.
Hand in hand with the formation of the veno-lymphatic channels, there occurs a condensation of the mesenchyme in their
immediate vicinity. The great accumulation of lymph in this
region has now found an outlet into the venous system through the
veno-lymphatic channels. The mesenchymal spaces are then
either absorbed by the veno-lymphatics, or their walls collapse so
that the tissue becomes much more compact than it formerly was.
Immediately surrounding the veno-lymphatics the condensation
has gone so far as to form definite walls for these channels.
The veno-lymphatic anlagen of the lymph hearts increase
rapidly in size, during the third and fourth weeks. A process of
absorption of the septa1 walls between the several anlagen takes
place during the later part of the fourth week. Beginning at the
anterior end and proceeding posteriorly, the several spaces fuse
with each other so that near the beginning of the fifth week, single
cavities are formed for eachlymph heart. In the meantime, muscle
cells have wandered in from the adjacent, muscle plates, completing the essential steps in the formation of t'he lymph hearts.
Fig. 2 is a representation of the veno-lymphatics of a twenty-five
day old embryo of the loggerhead turtle. The veno-lymphatic
channels still contain red blood cells. They are readily distinguished from the accompaning vein by their denser walls. Fig. 3
is a section through the lymph heart of a loggerhead turtle embryo
of thirty-two days development.
The results of this investigation show that the mesenchymal
spaces have an important function to perform in initiating the
development of the posterior lymph hearts. The importance of
the intercellular spaces is probably more clearly brought out in
turtles than in birds and mammals, because in the latter we are
dealing with more or less rudimentary structures. A study of the
development of the anterior lymph sacs of the turtle, itself,
would indicate as much. This, however, will be considered at
another time. In the highly specialized, or, in some cases, rudimentary lymphatic structures of birds and mammals, the earlier
stages are passed through too rapidly, and aqe too slurred or
masked to enable one to determine accurately the exact condition
of affairs. Even in the present series of turtle embryos, which
represent stages preserved at morning, noon, and night for every
day of development from the time of laying until hatching, it will
be necessary during the present summer to fill in certain critical
stages in order t o determine positively whether the veno-lymphatics represent true modified capillaries or not. There are indications that in the development of both the lymph hearts andthe
lymph sacs of the loggerhead turtle, the mesenchymal spaces
play an even more important part than has been assigned to them
in this paper.
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development, space, mal, relations, posterior, heart, turtles, lymph, mesenchy
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