140 MAMMALIAN SEXUAL CHARACTERS 



experiments that a given organ of internal secretion 

 has a certain function. The corpora lutea, for 

 example, according to one theory are ductless glands, 

 the function of whose secretion is to establish the 

 ova in the uterus and promote their development. 

 Another function suggested for the secretion of the 

 corpora lutea is to prevent further ovulation during 

 pregnancy. The evolutionist, on the other hand, 

 asks what was the origin of the corpora lutea, why 

 should the ruptured ovarian follicles after the 

 escape of the ova in Mammals undergo a progressive 

 development and persist during the greater part or 

 the whole of pregnancy ? It seems obvious that the 

 corpora lutea in evolution were a consequence of 

 intra-uterine gestation, for they occur only in 

 association with this condition, and it is impossible 

 to suppose that a mutation could arise accidentally 

 by which the ruptured follicles should produce a 

 secretion which would cause the fertilised ova to 

 develop within the oviducts. The developing ovum 

 within the uterus may, however, reasonably be 

 supposed to give off something which is absorbed 

 into the maternal blood, and this something would 

 be of the same nature as that which was given off 

 by the ovum while still within the ovarian follicle. 

 The presence of this hormone might cause the 

 follicular cells to behave as though the ovum was 

 still present in the follicle, so that they would 

 persist and not die and be absorbed. But this 

 leaves the question, what is lutein and why is it 

 secreted ? Lutein is a colouring matter sometimes 

 found in blood-clots, and probably derived from 

 haemoglobin. In the corpus luteum the lutein is 

 contained in the cells, not in a blood-clot. 



