THE RELATIVE POSTNATAL GROWTH O F THE SYSTEMS AND ORGANS O F THE CHICKEN1 HOMER B. LATIMER Department of Zoology and Anatomy, University of Nebraska TEN CHARTS The growth of the body, systems and organs of fhe singlecomb White Leghorn chicken has been described in a recent paper, but a comparison of the growth of the various parts with reference to the entire body growth was not given, and so this little study has been undertaken to show the relative changes in the growth of the systems and organs between hatching and maturity. MATERIAL AND METHODS The data on which this study is based are taken from a previous paper (Latimer, '24) in which is reported the growth of 100 single-comb White Leghorn chickens, raised at the University of Minnesota and ranging in age from day of hatching to 300 days of age, with three specimens about one year old and three about two years old. The details of the study of the growth in gross body weight and of the methods of making the autopsies are given in the earlier report and will not be included here. All of the weights in grams given in this paper were determined by using the empirical formulae given in the earlier report and the percentage values were secured by inspection of the percentage curves used in the preparation of the charts of the earlier paper. The percentage weight in all cases is the weight of Studies from the Zoological and Anatomical Laboratories of the University of Nebraska, no. 141. 233 THE ANATOMICAL RECORD, TOL. 31, NO. 3 234 HOMER R. IJATIMER the system 01-organ reduced to a percentage of the net hody weight, or the weight of the chicken immediately after killing millus tlie weight of the contents of the digestive tulx. The method of tletermining the ratios of the percentage weights is the same as that used by Doilaltlson ('23) in his study of the albino rat. I wish to express my thanks to the Departm c i i i t of Anntomy of the University of Jlirinesota f o r making possihle this series of studies 011 the gron-th of the chicken. TOTAL INCREASE I S \VFXGHT 'rlie total inorease in weight from hatching to maturity is not t l w samc for the various systems and organs of the cliickcii, but ranges from an increase of about sevenfold for the ctliitral iiervous sytclm t o a maximum of 214 times f o r tlie pancreas. The growth iiicrcases for the various parts are summlirizetl in table 1 . The first columii of' table 1gives the name of the organ o r system ; the secoiicl coIumIi, the hatching weight in grams, ; i l i t l tliv third column gives the weight at maturity. The last column gives the ratios of the weight at maturity to the 1i;itcliiiig weight. 'L'Eiese ratios greatly facilitate comparisoii of tlie growth in weight of the various parts. A study of tliis taltle will show that the integument and the gross body wt4glit each increase a little over 'TO times, a i d that there arc tweiitj- parts iiicreasirig less than 70 times and hut three wliicli increase more than the gross body weight. As is to be expected, those parts and organs which have a precocious development increase less in postnatal life. The central nervous system and the eyeballs increase but 6.6 times from hatcliing to maturity, followed by the hypophysis and thc bead of the females. A study of the postnatal growth of tlie ceiitral riervous system of the domestic fowl (Latimer, '25) shows that the braiii aiicl the spinal cord do not increase an equal amouiit between hatching aiid maturity, for the cord iiicreases 19 times during this period and the brain iiicreases but fourfold. There is a dieerelice in the total increase in tlw parts of the h a i n , although iiot so great a difference as that bch-eeii the brain arid the cord. 233 I'OSTNATAL GROWTH OF C H I C K R S The head of the male chickens increases over twicc as much as does the head of the females, but this is due largely to the heavy comb and wattles of the male fowls, the comb, wattles, and ear lobes being included in the weight of the head of both sexes. TABLE 1 libcrease in weight of the various oiyare and ajaienu, .--- ......... .. . -- ............... . ~. -. Nervous s m m ............ Eyeballs. Hypophgeia ............... Head (female) ............. 8tOmacli ................... Digeative tube ............. i! Gizzard..................... Int&n&q i j Head (male) Viscera. ................... i Suprsronala / Liver ...................... I Kidneye. Skeleton (female) ........... Skeleton(male) ............ 1 Heart ..................... j Spleen .................... .................. ' ................. .............. ............... ................... 1 Grow body weight.. ....... ................ ! Thyroid ................... : Muscnlature ............... Pancreas .................. Thymus .................... Feathers (female). ......... Feathem (male) ........... integument . .... ! -. - -- I I HATCHING PRIUliT IN BNAMS .- 1.00 0.80 0.0021 4.0 0.40 4.67 1 j 2.0 1.87 . 1 4.0 6.89 1 0.W 1.6 0.4 6.2 5.2 0.D 0.04 37.0 8.1 8.2 om26 0.02 1 I . . 1 1 ! j 1 53.2 5.78 107.8 60.2 Fio.6 112.8 1W.7 0.2454 60.9 15.3 201.2 254.1 13.7 2.58 2800.0 217.1 0.284 1257.3 4.B 1 ! ; i . 1 : 1 13.3 14.5 23.0 26.1 25.0 28.2 28.3 31.8 33.9 j 38.2 38.5 , 48.9 ' I! : 70.0.3 m.3 113.6 214.0 8 0.10 1.8 1.8 i.5 0.76 I i 64.9 M.Ci 61.3 81.6 .... The viscera increase a little over 28 times, or but a little more than the head of the male. The weights of the viscera as given in this table are the sums of the weights of the various organs, a list of which is given in table 2, which gives the ratios of the percentage weights. The lungs are not iiic~lutlctl, unfortunately, for after 1200 grams of gross body weight lhev were so variable that 110 formula was deduced and 1 1 0 CIII'VC' drawn. The weights of the two lungs and the tra(hea togctlier for each chicken are shown plotted on the chart in figiire 19 of the previous report. The male skeleton iiicreases more than the female skeleton, or 49 times for the male and but 39 times f o r the female skeleton. The male skeleton is followed by tlie heart, which increases 55 times and tlic spleen which increases 68 times, or nearly as much as the total body weight increase. The th;vroitl, the musculatnre, and the pancreas each increase more than the total body weight increase, the values are respectively, 114, 153, and 214 times. The thyroid and the pancreas each form but a relatively small part of the total body weight, but the skeletal muscles increase from 22 per cent of the net body weight at time of hatching to 48 per cent in the adult fowl. An increase of over 150 times in the absolute weight of a part forming so large a percentage of the entimi body weight would naturally account for the larger Iiiirn1)c.r of organs iiicreasing loss than 70 timcts, or the in(wvise for the entire body from hatching t o maturity. 1'11~ larg:.eillcl*eiis(?in the thyroid weight is clue in part, a t least, to t l i ~iiic.iused amount of colloid and the increase of 314 times f o r thcl paiicwas may bc due to some extent to the difficult?in i.t~moving2111 of the glaiid in the newly liatched chicks. ?'lit> iiicreasc, of the thymus aiid tlie feathers f o r tlie male ; i i d tlic female are listed as tlie last three organs in table 1, for although they increase, respectively, but 8, 48, and 65 times their hatching weights ut maturity, they do hare maxima much higlier than these figures earlier in their growth. Xt its maximurn the thymus is 61 times its hatching weight, or a little over 8 times tlie ratio at maturity. The feathers of the fernale a t their maximum arc 1.3 times the ratio a t maturity and the maximum for the male plumage is a little over 1.2 times the ratio at maturity. 237 POSTNATAL GROWTH OF CHICICES RELATIVE PERCENTAGE WEIGHTS The weights of the various organs and systems reduced to percentages of the net body weight are shown plotted against the gross body weight in the previous paper. The individual percentages were plotted on a preliminary chart and a mrve was drawn by inspection through the -. .. .. . .. GKOSS BODY w E w m IN . GKAMS I.IVF.I~ I .Oi 300 500 700 1100 1300 1500 1700 1900 2100 2300 2~ . . . . . . .. .. KIDBEYS TIIYXUS , 100 1300 .. . i I I O.!U 0.88 0.84 0.80 0.76 0.71 0.67 0.61 0.57 0.53 i +WIG , ~ 1 : I , j 1 1.00 1.83 1.w 1.81 1 . ti0 I .46 1.31 1.15 1.oti 0.99 0.91 0.88 0.80 0.73 ~ I 1 .00 0.97 0.84 0.75 0 . ti:) 0 . ti0 0.5i 0.58 j 0.m 0.65 0.66 0.66 0.66 I ! 1. 00 2.50 4.17 3.83 3.34 3.50 3.67 3.17 2.67 2.42 2.17 2.08 2.00 1.83 I i i ~ I ~ I 1.00 0.!)2 0.72 0.7ti 0.89 I 0.98 1.01 1.02 1.03 I 1.04 1.07 ' 1.15 *** * ** ~ ' I .oo 1.72 1.50 1 .25 1.@2 0.92 o.,o 0.69 0.64 0.58 0.56 0.56 I II I i I I 1.oo 1.05 1.27 1.47 I .tie 1.71 1. i 8 1.45 1.00 0.64 0.44 0.31 0.20 0.09 cloii~,lc-~~-c!ightctl mcdiaiis, o r the averages for hoth tlie p t ~ cwitage weight of the organ aiitl tlie gross 1)ocly weight for c.ac.11200 grams' iiicrease i i i body wiglit, aiid this curve witlioiit tliti iiidivitluul cases is showii a s the lighter line in the cliarts iii the previous paper. Thc percentage values read from tticse ~ i i r v e sw c i ~ilsetl in conipntirig the ratios f o r this iq)ort. 111 many cases tllc origiiial data \\-ere coiisulted in \. P 1-if i c i i t i ()II ( )f t 1I p ~ reii c t a gc s . 'l'li c 1)erc en t a ge we igI i t ;it Iiatcliiiig was takeii a s unity aiid the ratios of the percent;igw f o r each orgm a t 100 gr*arns aiicl for each 100 grams' iiicreaw i i i gross hody weight thereafter were tletermiiied. P'ig11rw 1 to 10 show t l ~ c wratios grapliically a11d tables 2 ant1 3 give tlic ratios for hatching, 100 grams and each 200 mxms ' iiicrensc iii g'i'oss body weight tlicreaftei-. 'I'liis t iwitmciit makes a cwmparisoir of tlic cliangcs iii tlie perwiitagw \ w - y much easier than N dircct iiispection of tlic i~wcciittigecurves. 'I'lit~ ratios for tlic viscera a i d the individual orgaiis whieli arv listed as viscera are given iii table 2. The sum of tlic ~)(weiitages of the inclividual organs given in this table werc iitltlt'(1, aiicl tlicse results were treated as were tlic pcrcwitagcs of tlie individual organs, aiid these ratios are given in the w ~ o i i ~cwlumii, l the gross hotly weights being given iii tlie timt columii. The ratios f o r the digestive tube, gireii iii tlie fifth eolumii, are the ratios for the sums of the parts of the cligestive tuhe, namely-, tlie stomach or Iwoveiitriculus, tlie giaxard mid the intestiiies, esopliagus, imtl the c w p d l weiglicd together. These parts are gilreii separately as well iis tlicir sum, mid 2111 the ratios ai'c for. tlie empty tligestil--e tube 01'its parts. To complete tlie list, the luiigs a i d trac1ic.a 4 1 o i i l ~ lbc inrlu~led,h i t , as previons1)- stai ecl, they were S O varialde in weight that it did iiot seem wise to iiiclude them. r!'11(31~~~ were 1 1 0 apparciit pathological luiigs in the group-at least, 110 pathological specimens w r e noticed in making tlitl autopsies. ' h e ten viscera (male and female together) listed in table 2 forin 21.4 pcar writ of tho net hotly weight at time of hatching. ch 239 POSTXATAL GROWTH OF CHICICES This rises to 21.7 per cent at 100 grams oP body weight aiid then slowly decreases to 8.3 per cent in the adult. These ralues of course do not include the percentage weight of the lungs and the submaxillary which are included by Donaldson ('23) in tlie percentage weights of tlie viscera of the albino rat. The viscera of the male albino rat form 10.9 per cent of the body weight at birth, 19.2 per cent at 25 grams of body weight, and then decrease to 10.5 per cent in the adult. These figures shou~that at birth tlie percentage weights of the visTABLE a f?c.lativua perccntage weigkta of the puvtr and syrtems - . .. I _ ... ........ . . . FEATHI<Krl (SALE) . 1 .OO 0.63 0.33 0-26 IKW) 1100 1300 1500 1700 1 0 21100 m ''ti00 0.20 j 0.17 0.15 0.14 0.12 0.11 0.11 I 0.097 ' 0.090 0.081 ' 1 ....... 1.oo 0.68 0.41 0.33 0.29 0.25 1.00 0.66 0.41 0.41 0.37 0.23 0.21 0.31 0.29 0.21 0.30 0.19 0.31 0.33 0.18 0.33 0.18 0.18 0.18 ' . 0.34 0.37 . .. - 1.OO 1.07 1.07 1.8 1.06 0.76 0.68 0.83 0.60 0.68 1.01 0.96 0.89 0.82 0.76 0.74 0.69 0.40 0.68 0.65 - .. . . . - ......... 1.oo 1.07 1.Oi 1.09 1.05 1.w2 0.89 1.QL 1.02 : I ._. . . . . . 1 .oo ....... 1.41 1.75 1.87 1.96 2-00 2.04 1.oo 1.41 2.00 2.16 2.24 2.40 2.66 1.00 1.41 2 .00 2.16 2.24 3.40 2.65 2.07 2.54 2.10 2.12 2.14 2.16 2.17 2.00 1.69 1.38 1.10 2.59 2.64 2.40 2.16 1.84 I .67 2.19 . . . . . .- _. . . . . . . . . . . . . (exc-clding the lungs) are just a little less than twice as great as those of the viscera in the rat. The maximum percentage weights are more nearly alike, for the chicken viscera are now hut slightly heavier than the viscera of the rat. At maturity the viscera of the rat form a larger percentage of the body weight than d o the viscera of the chicken. Similar data are given in table 3 for the systems and parts of the body iiot listed as viscera. The central iiervous system is given all togctl~erhere, as a study of the growth of the 1 240 HOMER B. LATIMER parts of the brain and of the spinal cord of the chicken has been published (Latimer, '25). As stated above, the values used in determining the ratios given in tables 2 and 3 and plotted in figures 1to 10 are taken from the curves drawn by inspection. There are, of course, individual variations in the percentage weights and these are referred to in the earlier paper, the curve merely giving the Fig. 1 The percentage weights of the eyeballs (upper curve) and the hypophysis (lower curve) reduced to ratios of the percentage weights at hatching plotted against gross body weight in grams. median values for each body weight. A careful study of the distribution of the cases for the digestive tube shows that the percentage growth of this part increases for the first six days and that there is also a similar very brief rise in the percentage values of the liver (fig. 5 ) . The curve for the entire digestive tube is not shown. It follows the curve for the gizzard (fig. 4) very closely, and so it was not drawn on the chart. The data are given in table 3. It will readily be seen by a study of the curves in figures 1 to 10 that thcre arc four types of curves. There are, first of all and found in the largest number of cases, the curves which decline from hatching to maturity. Included in this type are the central nervous system (brain and spinal cord), eyeballs, hypophysis, glandular stomach o r proventrieulus, entire digestive tract, gizzard, head (both male and female), Fig. 2 The percentage weights of the suprarenals (upper curve) and the entire central nervous system (lower curve) rrduced t o ratios of the percentage weight at liatching plotted against gross bod? weight in grams. suprarenals, and the heart. While the heart is listed in this group, it does show a rise toward the latter part of the period, f o r after a minimum ratio of 0.57 at a gross body weight of 1300 grams the ratio slowly rises to 0.6G at 2100 grams and remains at this level up to maturity. I n the second group of curves are those which rise to a maximum after hatching and then later decrease t o a ratio less than unity, or to a smaller percentage of the net body weight than at hatching. This group includes the following : I ) R I I ~ I ’ C R S , liver, iiitcstiiics (including esophagus a i d crop), i4scchr.n (sum of organs listed in table a ) , lcidncys, ligamenl011s skelctoii (hot11 male and female), and tlie tliymns. 111 the thii-d group a3.e listed tlic two orgaiis which rise t o i\ maximum after liatcliiiig and theii clecroase slightly, hut whosv ratio I-emains greater tliaii niiity, or wliicli form R larger. pt!rcmtage of tlie net body weight even at matuvit? tlitlii they (10 at time of Iiatcliing. The feathers a i d the spleen t\vo ciii*vos iiiclutled iii this group. E’igurc 10 slio\vs t l i a t t h e fcmt.ilc plumage w t i i i m to I ~ C R I ’tlic ~ ~ same p e i ~ c i i t age of the net body weight at maturity as it formed a t liatcliing. The mrw showing the ratios of the percentage weights ot’ t ~ i esplccn (fig. 8 ) shows-two maxima, the first wliicli is also the most marked at 300 gi-ama of gross body ~veiglit t i i d tlic second a t 1000 or 1100 grams of gross body weight. The fourth group, or those p a r t s with a ratio greater than imity or a larger perceiitage of thc net body weight at rn:it~ii*itytlim at time of Iiatching, iiicludes tlic thyroid and >ii*ih tlich 243 POSTNATAL GROWTTI OF ('HICYEN tlie muscnlature. Tlie thyroid (fig. '7) drops to a minimum ratio of 0.72 at 300 grams of gross body weight, but rises thereafter., attaining a maximum ratio of 1.15 at 2100 grams of gross body weight. After this body weight the thyroid was so variable that. it seemed best to carry the curve to this point only. PER.IODS O F MAXIMIJM PRBCESTAGE WEIGHTS Table 4 g i w s the gross body weights at which the maximum percentage ratios occur for the various organs. There are TABLE 4 H o t l ! ~ moiglit.s at zclaich tlie organs nrirl systeiibs attain their maxintum percentage weight ..... .. .. . . .. .. ... I . .. . .. ' - on(iAxs -. Kcrvous systeiii ' Hypophysis E yehalk Tlatching or 37 grmis Head (male and feiiiale) ITeart Suprarenal~ Gizzard StomRrll ' Digestive tnlie ' "' Skeleton I I Thyroid J l ( K ) grarriM ?(%XIgrams Thymus Feathers I ?olusculatare Pancreas Liver Iritestiiiex Viscera 100 grmw .. . Kidneys Spleen 300 grams ... iiiiie organs and s p t e m s of the chicken wliich have this maximum percentage at time of hatching. The braiii arid the spinal cord are here takcii together, but each, as previously shown, has its maximum percentage of the net body weight at time of hatching. This initial maximum is found in the case of the eyeballs, the hppophysis, the head, the heart, and the entire digestive tube. The maximum f o r the digestive tube, as described above, really comes on the sixth day. A comparison of this tahle with table 1 given by Donaldsoii ('23) shows that of these nine entries in table 4, but one, the li~-pophysis,forms its maximum pereelitage at birth in the alhino rat. Donaldson gives the luiigs, the Iiypophysis, and the tliyroitl as forming their maximum percentage weight a t birth in the rat. IiIxamination of the percentages of the chick luiigs sliows that they, too, might be included in this list, for \vitliont tloulif their maximum percentage weight occurs at F'ig. 1 The ratios of gizzard (middle curve), weight in grams. The folloas very elost4y the the l'arts of the digestive traet, intestine (upper curve), and stomach (lowest currej, plotted against gross body curve for the entire cmpty digestive tract (not shown) curw for the gizzard. t i r w of hatcliiiig. Tliis would make two orgaris witli 8 commoil maximurn percentage weight a t birth in the chick and iii tlie alhirio rat, namely, the lungs and the hppophysis. The pcrcwitage of the thyroid does decrease for a time in the c*liick (fig.7 ) , but it later. increases t o a greater relative weight a t 2100 grams. The maximum relative weight of the lieart of the chick at hatching may be explained by its grcater activit!- compared with that of the ncw.horn rat, thus necessitat- POSTXATAL GLtOTVTH OP C€€ICI<EN 245 ing a much more effective circulation in the chick. Joseph ('08) has suggested that the activity of an animal is directly correlated with its heart size. The precocious development of the digestive tube in the chick may be explained by the differciice in the diet--.the rat is nourished by the maternal Fig. 5 The ratios of the pancreas (upper curve) and the liver below plotted against gross body weight in grams. milk, while the chick must eat nearly the same diet as the adult, and hence it needs a digestive system fully able to care for this complex food. Donaldson ('23) finds the maximum percentage weight of the digestive tract of the rat at a body weight of 31.1 grams, or a t about six times the birth weight. Jackson ('13) finds the head of the albino rat reaching its maximum relative weight at seven days, but in the chick this maximum occurs a t liatching. This may be cxplairiotl by tlie better development of the eyes and central nervous sysiii the chick, agaiii illustrating the better development of the chick at time of hatching compared with the albino rat, tchm Fig. 6 The ratios of tlir percentage weights of the musculature and tlw kitlnrys plotted against gross body weight in gr:irns. The curve whic.11 rises cwiitiiiuouuly is that of the musenlnture. whicah is born blind arid dependent upon maternal protectioii arid food supply, while the chick, if supplied with a sourcc of artificial heat for part of tlie time, will get along fairly well. The suprarenals of the rat reach their maximum pcrwntage weight when the body is about five times its birth weight, hut in the chick they are relatively largest at hatching. POSTNATAL GROWTH O F CHICKEK 247 The pancreas, liver, intestines (including esophagus and crop), and the sum of all the viscera attain their maximum at 100 grams of gross body weight. The spleen and the kidneys do not attain their maximum percentage until a body weight of 300 grams is reached, or at about forty days of age. This retardation in the attainment of the maximum percentage weight of the kidneys may be due possihly to t h o emhryonic elimination of the nitrogenous waste through the allantois and the fact that the kidneys do not function very extensively until after hatching. Figure Pig. 7 The ratios of the thyroid and the heart plotted against gross hody weight in grams. 8, which shows the graphic representation of the ratios for the spleen, shows two maxima, one which is the greater, at 300 grams and another a t 1000 or 1100 grams of gross body weight. The skeleton reaches its maximum percentage weight at 500 grams, o r between sixty and seventy days of age or slightly after the end of the period of most rapid percentage increase of the skeletal musculature. Jackson and Lou-rey ('12) report a slight increase in the percentage weight of the skeleton of the albino rat during the first week of postnatal life, and then, following this maximum, the percentage neiglits tlecrc~asc to maturity. ‘I’hc musculature does not reach its maximmim iiiitil maturity, I)nt its period of most ral)i(l i*cllati\rc growth is passed hy the time the 1)ody has attwiiitd ;I weiglit of about 300 grams. It is iiiteresting to iiotti that the maximum percentage wciglit of tlie cerebellum ( L a t h e r , 9 5 ) also occurs at from 400 t o 600 grams of gross hotly iveiglit, suggesting the similarity in relative tlcrelopmcwt of the skeleton, musculature, and the cwebellnm. b’ig. 8 The mtios of tlie perceritngr wciglits of the spleen plotted :(gainst gross lrody weight iii gmiiix. The scale of tlic oidiiintes liere is onc’ Irnlf that o f l l i r otlicr fig1irc.s. 1 lie thymus aiicl the feathers present similar ratio c u r w s , t ~ c c p tthat there is a sex tlifreiwice in tlic Iwrceiitagcs of t h e feathers and iioric in the Case of tlie t h j ~ n n s . Rotli reach tlitair rnaximum relatirc weight at 1100 grams, o r at the same time as the sccoiicl maximum for the spleen. Riddle in a iwwit pnblication, has describetl a growth curve of the thymus in pigeons similar to tliat of the chiclien. The relative weights of the thyroid are showii in figure 7 from hatchiiig to 2100 grams of gross body weight only, f o r r 1 (’as), after this time the weights of the iiitlividiial thyroids varied to sucli an extent that it seemcvl hest to exclude these weights POSTNATA4L GRO\T'TH O F CHICKEN 249 as unreliable. Some of tlie heavier adult thyroicls map have been pathological, and so, while the individual weights arc indicated in figure 2 1 of the earlier paper, tlie formula aiid the data are carried to 2100 grams of gross body weight only. The musculature increases up to maturity. Some of this increase in the older chickens may be due to an iiicreased amount of fat stored within the muscle and which could not Fig. 9 The ratios of the skeleton (ilbove) and the head (Lclow) plotted :igainst gross body weight in grams. Both curves show ii sex differeiice in the 1:jtter purt, the UTJPW p r t of cwch repwscwts tlic iatios f o i t h e nialt~sa n d tho lower, the females. he separated mechanically from t h e muscle tissue. .Jtwkson and Lowrey ( '12) find the musculature of the newborn albino rat forming 24.4 per cent of the net h d y weight. Tn the one-week-old rat thev find this percentage reduced to 22.8 per cent, and following this an increase to 45.4 per cent in the adult. The chicken musculature iiicrcases continuously from 22 per cent a t time of hatching to 18 per cent a t maturity. T I i L I N A T O Y I C ~ LRECORD, Yola. :II, YO. '! 250 HOMER B. 1.ATIMER TIIF: LIFE CYCLE IK THE CIIICKEK' A N D I S M A S 1)oiialdsoii ( '18) has sliowii that from hirth to old age mail tievelops one-thirtieth as fast as tlie albino rat, but the gi-owth of the chicken docs not show a constant ratio to the grou-th of' mail. The comparisoii of the growth of tlie chicken arid of mail for six periods is shown in table 5. During the fimt two pc'riods, or tlie embryonic period and the time iii ~ ~ i i i ctlie l i loirtli weight is doubled, the chicken is growing 1 3 times faster than mail. After this tlic growth is accelerated in tlic chick, as cwmparetl with the liuman growth, f o r the chick triples its hatching weight in twentythree days aiid miiii in oiie year, or oil(\-sixtceiilli tliri time required by man. TABLE 5 (:,nwth of the chicken conipaietl uitk t h a t of man I ' 1~1~1<1011~ CHICKEN ........ b h i I I r yo11ic ' \TAN RATIO .'I ............................... I ) c d ) l t ~birth weight. ..................... Tlime t.imes birth .weight................... Pnl1crtg ( fe1ll:llr) . . . . . . . . . . . . . . . . . . . . . . . . . cirowth in length CC'~LRCS................... l..)ltl>lgc.................................. This acceleration is further iiicreased in the comparisoii of thc times of pnberty f o r tlric female of both species and for tlic time of tlie cessatioii of iiicrtmc in body length. 111 both of these tlie ratio is one-thirtieth, or these two periods are rcwalictl by t l i c c,liic*Bin ono-thirtieth the time required by man. T l i c b time of pu1)crt.y is given as six months for the females oiily, as this period can be more easily determineci in the female fowl. !J'his age may be a little too early, a i d yet in both tlie chick and in man there is a wide variation in the ago of pulwrty, a l i d so hoth are merely approximations. Sclincidcr ailti Duiin ( '24), in their study of the lengths of the boiicls of Ihe fowl, conclude that the bone length is comp l d c d by eight rnoiitlis of age in the Tleghorii. The slreletoiis of the prcsent series of cliickcns ase being studied (Latimer, POSTNATAL GROWTH 014’ CHIC’I.il3N 251 ’23) and the ossifications of the long bones are all completed before the two hundredth day, so the cessation of growth in length is placed at eight months f o r the chick. The last period, or the age of the chicken comparable to ninety years in man, is more difficult to determine, for Fig. 10 The ratios of the feathers (above) and the thymus (lower eurvcj plotted against gross body weight in grams. The curve for the feathers shows a sex diffrrenee after 1100 grams, the upper arm of the curve rcprcsrnting the ratios for the males and the lower, the females. chickcns usually do not die of old age, and so this is more o r less an approximation. Seven years may be too young. I have learned of two bantam hens which lived to be ten and twelve years old, and the one which was accidentally killed at ten years layed up to nine years of age. The men in our Poultry Hnsbandry Department feel that seveii years is R fnii. cstimate, altliougli there seem to be 1 1 0 tlefiiiite data 0 7 1 this point. 3 1 1 age greater than seven years for tlie chicken tvoiil(1only accentuate the point of the chart, namely, that thc time of old age i u tlie chicken comes back to the same ratio i t s the first two periods or possibly less tlla~lthis ratio. \Ire may coiic~ludcthat the cliickeri matures more rapidly, thus leaving a relatively longer period of maturity than is fonncl in man. The cliiclteii urliicli belongs to ti lower order of vertebrates thus has a shorter period of growth a i d a relativcly longer period. of mature life when c,ompai*etlwith tlic glY)\Ytll cycle of mall. SIJ M1\1A K 1- 1. The gross body m-eight of the cbickeii increases 70 times fiwm liat~hiiigto maturity. The central nervous system, e:-cl)w11s, a i d liypopliyais iiicrease but about 7 times, all tho viscera together increase 28 times, and but three structures, t h o thyi*oicl,the musculature, a i d the pancreas, increase m o i ~ tlian 70 times. 2. ‘Plie percentage weiglits of the systems aiitl organs ITtliiced to ratios of tlie percentage weiglit a t time of liatcliiiig fall into fonr groups : a ) those parts TTThiCh decrease from liatcliiiig to less than the hatching percentage a t maturitythis group includes the larger numher of systems and organs ; 1)) those parts wliicli rise to a maximum after Iiatcliiiig, Init a t matnritp hare a smaller percentage than a t time of hatching; the third group iiicliides hut two organs, the feathers a i d tlie splceii, each of which rises to a maximum after hatcliiiig, but d o s c percentage remains greater than tlie hatching pcirceiitage at maturity, iliid, d ) those pitrts wliicli rise t o tlicbir maximum a t maturity. 3. Tell systems a i d organs i i i the chickeii have their maximum percentage at time of hatching. This sliows that more oi-gaiis in tlic c4iick develop earlier than in tlie rat, due probaldy to the more active aiitl iaclcpeiitlent life of the chick immediately after liatching. (a) POSTNATAL G R O W T H OF C H I C K E X 253 4. A comparison of the life-cycle in the chick and in man sliom7s that the development of the chick increases in rapidity when compared with the development of man, thus leaving a relatively longer period of mature life in the chicken. BIBLIOGRAPHY DOXALDSON, 11. H. 1918 A comparison of growth changes in the nervous sys tem of the r a t with corresponding changes in the nervous system of man. Proe. Kat. Acad. Science, vol. 4, pp. 280-283. -___ 1923 On changes in the ielirtive weights of the viscera an d other rat. Am, Jour. Physiol., vol. organs from birth to maturity-albino 67, pp. 1-21. JACKSON, C. M. 1913 Postnatal growth and variability of the body an d of the various organs in the albino rat. Am. Jour. Aiiat., vol. 15, pp. 1-68. JACKSON, C. M., AND LOWREY, L. G. 1912 On the relative growth of the component parts (head, trunk and extremities) and systems (skin, skeleton, inusculature a n d viscera) of the albino rat. Anat. Rec., vol. 6, pp. 449-474. 1908 The ratio between heiirt-wright an d body-weight in various JOSEPH, D. R. animals. Jour. Exp. Med., vol. 10, pp. 521628. LATIMER, H. B. 1921 The growth of the organs and systems of the single-comb White Leghorn chick. Anat. Rec., vol. 21, p. 70 (abstract). 1923 The growth of the skeleton and some of the individual bones of the single-comb White Leghorn chicken. Anat. Rec., vol. 25, p. 139 (abstract), 1924 Postnatal growth of the body, systems an d organs of the single-comb White Leghorn chicken. Jour. Ag. Research, vol. 29, pp. 363-397. 1925 The postnatal growth of the central nervous system of the chicken. J o u r . Comp. Neur., vol. 38, pp. 251-297. EIDDLE, OSCAR, AND FREY, PAUL192,5 The growth and age involution of the thymus in male and female pigeons. Am. J o u r . Physiol., vol. 71, pp. 413-429. SCHNEIDER, MARGARET, AND DUNN,L. C. 1924 On the length and variability of the bones of the White Leghorn fowl. Anat. Rec., vol. 27, pp. 229-239.