MAMMALIAN SEXUAL CHARACTERS 141 



Chemical investigation shows that the lutein of 

 the corpus luteum is almost if not quite identical with 

 the colouring matter of the yolk in birds and reptiles. 

 Escher ^ found that the lutein of the corpus luteum 

 had the formula C4QH5g and was apparently identical 

 with the carotin of the carrot, while the lutein of 

 egg-yolk was C4oH5g02 and more soluble in alcohol, 

 less soluble in petroleum ether, than that of the 

 corpus luteum. The difference, if it exists, is very 

 slight, and it is evident that one compound could 

 easily be converted into the other. Moreover, the 

 hypertrophied foUicular cells which constitute the 

 corpus luteum secrete fat which is seen in them in 

 globules. The similarity of their contents therefore 

 to yolk is very remarkable, and it may be suggested 

 that the hormones absorbed from the ovum or 

 embryo in the uterus acts upon the follicular cells in 

 such a way as to cause them to secrete substances 

 which in the ancestor were passed on to the ovum 

 and formed the yolk. It may be urged that this 

 idea is contradictory to the previous suggestion that 

 the absorption of nourishment by the intra-uterine 

 embryo was the cause of the gradual decline of the 

 process of yolk-secretion by the ova in the ovary, 

 but it is not really so. Originally in the reptihan 

 ancestor, or in the Monotreme, the ovum in the 

 follicle secreted yellow-coloured yolk. The materials 

 for this, at any rate, passed through the follicle cells, 

 and it is probable that these cells were not entirely 

 passive, but actively secretory in the process. 

 Substances diffusing from the ovum would be 

 present in the follicle cells during this process, and 

 probably act as a stimulus. The same substances 



1 Ztschr.f. Physiol Chem., 83 (1912). 



