120 CARNEGIE INSTITUTION OF WASHINGTON. 



increases the rate of carbohydrate metabolism, has also been found to de- 

 crease the size or storage metabolism of the ova. Mr. Walter Fisher has 

 collaborated in this study. It was found that a dosage compatible with 

 continued ovulation, and strictly limited to twice-daily injections during the 

 last half of the growth period of the ovum, reduced the size of ova of 9 birds 

 during a season by 2.8 to 5.7 per cent; and that the portion (one half) of 

 these eggs which was subjected to the effects of insulin during 40 hours longer 

 than the other half showed a further reduction of 4.1 per cent. 



From the first of his studies Dr. Riddle has been led by other kinds of 

 evidence to interpret high storage values of the yolk to mean low oxidizing 

 capacity. Still further confirmation of this interpretation has, therefore, 

 been obtained from both of the above studies. Other earlier work has shown 

 a correlation of large yolk-size with femaleness and of small yolk-size with 

 maleness in the embryos arising from such yolks. 



Origin of Single- Yolk Twins. 



Out of approximately 20,000 incubated eggs of doves and pigeons there 

 have arisen 8 cases of twin embryos, all apparently well formed. These 

 twins arose out of stock so closely watched and intensively studied as to 

 afford very exceptional information concerning the conditions attending their 

 origin. A control is afforded by the simultaneous determinations of yolk- 

 weights in 20,000 cases, yolk-analyses in 1,300 cases, and bomb-calorimeter 

 measurements of energy storage in 500 other eggs. Compared with the 

 control, 5 of the yolks that gave rise to twins were of extremely large size 

 and 3 were of extraordinarily small size. There is no reason for thinking 

 that the twin production was caused by an accidental cooling of the blasto- 

 derm, a condition suggested by Stockard as the real cause of twin production 

 in the fowl. Indeed, the experimental subjection of 231 embryos obtained 

 at from 4 to 24 hours of prematurity (Year Book, 1922, p. 121) to low temper- 

 atures before and during gastrulation yielded no case of double embryos, 

 though it did produce other kinds of abnormalities. Indeed, not only retarda- 

 tion but also acceleration of the developmental rate produces such abnormal- 

 ities. The large twin-producing ova were doubtless examples of an extremely 

 low metabolic rate in the unsegmented ova, and the small ova were examples 

 of an extremely high metabolic rate. Twins arose in these eggs as a result 

 of this retardation or acceleration already present in the ovum at the time 

 it left the ovary. 



Among agents that induce abnormalities and monsters in early embryos 

 of the pigeon, high concentration of carbon dioxide comes first, then increased 

 concentration of oxygen, decreased oxygen, and low temperature last. Dur- 

 ing the first 2 to 4 days of development after laying it is the youngest stages 

 that are most affected by increase of carbon dioxide and of oxygen. The 

 later stages are relatively more effected by low temperature. Evidence is 

 supplied that a temperature of 39.4° C. (103° F.) is higher than the optimum 

 and produces a stimulating or accelerating effect during the first 12 to 24 

 hours of development after the egg is laid. Probably in consequence of 

 this accelerated development, the subjection of embryos during this 

 first 24 hours to exceptionally lowox ygen pressure results in a low survival 

 rate, and exceptionally high oxygen pressure results in a high survival rate. 



