author's abstract of this p.u>er issued 

 bt the bibliographic service, may 4 



A DEMONSTRATION OF THE ORIGIN OF TWO PAIRS 



OF FEMALE IDENTICAL TWINS FROM TWO 



OVA OF HIGH STORAGE! METABOLISM 



OSCAR RIDDLE 

 From the Station for Experimental Evolution, Cold Spring Harbor, L. I., N. Y. 



THIRTEEN TABLES 



Much has been written on identical twins; but, assuming that 

 it is a fact that such twins arise from the first two blastomeres of 

 a single ovum, not a single fact seems to be known concerning 

 either of the first two questions which one is tempted to ask con- 

 cerning the germs from which such twins arise. Probably the 

 first of these questions is. If identical twins arise from two sep- 

 arated blastomeres, why do the blastomeres separate in these 

 special and particular cases? Second, What functional differ- 

 ences characterize two such ova that produce male twins in one 

 instance and female twins in the other? It is possible that the 

 data presented here do not supply us with a fact concerning the 

 reason for the separation of the two blastomeres in these occa- 

 sional instances. A suggestion on this point is offered. But 

 the present data do, beyond question, give us a fact concerning 

 the functional status of two particular germs which produced 

 two pairs of female identical twin ring-doves. 



In my earlier studies- on the eggs (yolks) of doves and pigeons 

 it was learned that males arise from eggs (yolks) of lesser storage 

 metabolism (small size, and higher metabolism), and females 

 from eggs (yolks) of greater storage metabolism (large size, and 



^ High storage metabolism is to be interpreted as low (oxidizing) metabolism. 



2 See, a) Science, N. S., vol. 35, pp. 462-463, March 22, 1912; b) Carnegie Year 

 Book, no. 12, p. 322, 1913; c) Bulletin of the American Academy of Medicine, vol. 

 15, no. 5, pp. 265-285, October, 1914; d) American Naturalist, vol. 50, pp. 385-410, 

 July, 1916; e) Journal of the Washington Academy of Sciences, vol. 7, no. 11, June 

 4, 1917; f) Science, N. S., vol. 46, pp. 19-24, July 6, 1917. 



227 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 26, NO. 2, 

 JULY, 1918 



