368 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



Double-yolked Eg-gs.* — Mayiiie S. Curtis has made a study of 

 double-yolked eggs in hens. In one type (16 'OS p.c.) tliere is an entire 

 set of egg envelopes common to the two yolks ; in a second (70 'DO p.c.) 

 the chalaziferous layers are separate, but all or part of the thick 

 albumen is common to the two yolks ; in a third (12*98 p.c.) the yolks 

 have entirely separate thick albumen envelopes, but a common egg 

 membrane and shell. There are many gradations within and between 

 these groups. 



It is probable that the two components of the double-yolked egg 

 unite at any level of the oviduct from the funnel mouth to the isthmus 

 ring, and thus different types arise. In 36 ••44 p.c. of the double-yolked 

 eggs the ovulations which furnished the two yolks must have been 

 separated by an abnormally short interval, since a normal egg had been 

 laid on the preceding day. Examination showed that the two yolks 

 have passed the entire length of the duct together in only 16 •"28 p.c. 

 of the cases in which ovulations are known to have been unusually 

 rapid. Only in a small percentage of double-yolked eggs is there any 

 evidence of simultaneous ovulation. The fusion of follicles and a 

 resulting common blood supply is by no means the usual cause for the 

 production of a double-yolked egg. The occurrence of doul:)le-yolked 

 eggs may indicate heightened fecundity or a low physiological tone of 

 the oviduct. 



Pituitary Extract and Ovarian Activity.! — Raymond Pearl and 

 Frank M. Surface have previously shown that the substance of the 

 corpora lutea of the cow has the power to inhibit ovulation in an 

 actively laying fowl. They have sought for some other substance that 

 would activate the resting ovary. Then it would be possiljle to start 

 and stop a hen's egg-laying activities at will. Tlie connexion of the 

 pars anterior of the pituitary body with the genital organs has been 

 proved, and extract of pituitary body was experimented with. But the 

 injection of the substance into the abdominal cavity of hens, in which 

 the ovary was in a completely resting condition, did not cause any 

 activation of the ovary, in the sense of inducing ovulation at an earlier 

 date than that at which it would normally occur. 



Sex-changes in a Cow4 — Raymond Pearl and Frank M. Surface 

 describe the assumption of male secondary characters by a cow with 

 cystic degeneration of the ovaries. The cow was initially a perfect 

 female, bearing calves, and making a very high milk record. Later she 

 failed to come on heat, and gradually, but finally to a very marked 

 degree, took on male secondary characteristics, both in behaviour and 

 structure. The bull characteristics were best seen in the neck, which 

 developed a well-marked crest. The udder shrunk to a very small size. 

 The hips and rump took on the smooth, rounded, filled-out appearance 

 which is characteristic of the bull. 



* Journ. Agric. Research, iii. (1915) pp. 375-86 (7 pis.). 

 + Journ. Biol. Chemistry, xxi. (1915) pp. 95-101. 



X Rep. Maine Agric. Exper. Stat., 1915, pp. 65-80 (10 figs.). See also Science, 

 xli. (1915) pp. 615-6. 



