24 SUMMARY OF CURRENT RESEARCHES RELATING TO 



twins were very large compared with all the others produced by the 

 particular parents (totals of 116 and 134 eggs). The possibility of 

 double-yolked eggs is excluded because in pigeons their production is 

 practicolly restricted to hybrids from wider crosses, or to birds showing 

 striking reproductive abnormalities, or both, and these would not be 

 expected to appear in the two series in question. It is suggested that 

 the blastoderm-borders will be abnormally raised in extraordinarily large 

 eggs and abnormally lowered in extraordinarily small ones, and that 

 this might be the physical cause of the establishment of two independent 

 foci of development. If male identical twins were to be found develop- 

 ing from a very small egg it would furnish an interesting corroboration 

 of the author's theory. Meanwhile he thinks the data point clearly to 

 the conclusion that each pair of female identical twins arose from a 

 single ovum of high storage metabolism. J. A. T. 



Blood-fat and Egg-production in Fowls. — Oscar Eiddle and 

 J, Arthur Harris (Jonrn. Biol. Chem.,ldlS, 34, 161-70). Criticiz- 

 ing the conclusions of Warner and Edmond, the authors point out that 

 there is a progressive change in the nature of the correlation between 

 fat content in the blood of fowls and the total egg records, which is 

 positive for birds in a laying condition, sinks to zero after the cessation 

 of laying, and finally takes a high negative value in birds which have 

 long since ceased to lay. J. A. T. 



Effects of Quinine on Production of Yolk and Albumen. — Oscar 

 Riddle and Carl E. Anderson (Amer. Journ. Physiol., 1918, 47, 

 92-102). When small doses of quinine sulphate are fed to laying ring- 

 doves (Streptopelia risoria, S. alba, or hybrids of these), the yolk size 

 and total size of the eggs i^roduced are much decreased. Quinine has a 

 known tendency to reduce the destruction of the nitrogenous components 

 of the tissues, as measured by the recovery of nitrogen in the urine. 

 This probably applies to the secretory activity of the pigeon's oviduct, 

 where the product is entirely of protein nature. Furthermore, the 

 presence of quinine in the eggs checks the characteristic transformation 

 of nitrogenous compounds. The reductions and fluctuations in size of 

 the ova are consonant with the view that, in these cases, the size 

 attained is governed by restrictions placed upon the protein metabolism 

 rather than upon the general metabolism. J. A. T. 



(Estrous Cycle in Rats. — J. A. Long (Froc. Amer. Soc. Zool. in 

 Anat. Record, 1919, 15, 352). The length of the cycle averages nearly 

 five days. It is marked by changes in the vaginal and uterine mucosa 

 and by the liberation of ova from the mature follicles. The minute 

 changes are described. The uterus, besides exhibiting changes in its 

 mucosa, becomes at the beginning of the cycle greatly distended by the 

 secretion of clear fluid, in which the spermatozoa become very active. 

 The uterine mucosa is regenerated, at least in part, by mitosis of its 

 oells. Suckling may delay the second ovulation following parturition 

 about 40 days. The first ovulation follows the opening of the vagina 

 by about a day or two. During the first few weeks following puberty 



