466 LIFE : OUTLINES OF GENERAL BIOLOGY 



Female Organs. — There is not yet any unanimity on the part 

 of investigators as to the presence of "interstitial tissue" in the 

 ovary, but it is generally agreed that an endocrinal function is dis- 

 charged by what are called the corpora lutea in mammals. 



An ovarian ovum or egg-cell in a mammal lies within a nest of 

 cells — the Graafian follicle, which de Graaf himself mistook for the 

 ovum itself. When the egg is mature the follicle bursts, and the 

 empty nest is invaded by follicle-cells, which form the corpus 

 luteum. If the liberated ovum is not fertilised or is not fixed after 

 fertilisation to the wall of the uterus, the corpus luteum, after 

 developing a little, undergoes retrogression and disappears. But if 

 pregnancy occurs, the cells of the corpus luteum develop rapidly 

 (filling with lipoid granules of a yellow colour, to which the word 

 "luteum" refers), and a further ingrowth from the wall of the burst 

 follicle establishes connective tissue and blood-vessels. The endo- 

 crinal function of the corpus luteum then sets in. Its internal secre- 

 tions evoke changes in the wall of the uterus, which aid in the 

 fixation of the ovum and in the development of the placenta. In 

 some cases it seems to have been proved that the influence of the 

 corpus luteum is a sine qua non of the ovum's fixation and develop- 

 ment. Another function of the corpus luteum in the pregnant 

 mammal is the stimulation of the development, and even activity, 

 of the mammary glands. 



Many facts point to the conclusion that the ovary of Vertebrates 

 in general produces an internal secretion, analogous to that of the 

 testes, and determining the secondary sex-characters of the female ; 

 but the effects of spaying the female are not so marked as those 

 which follow the castration of the male; nor, as we have mentioned, 

 is the seat of the formation of the ovarian autacoid so clear as in 

 the case of the testes. It is probably included as a differentiated part 

 of the conni'Ctivc tissue framework or stroma of the ovary. 



Removal of the ovaries tends to inhibit the development of such 

 female organs as the uterus and the mammary glands, and also to 

 induce stoutness. 



In some types, such as birds, it seems certain that the inheritance 

 of the female organism includes the potentiality of various mascuhne 

 characters, whose expression or development is believed to be kept 

 in check by an inhibiting hormone (chalonc) from the ovary. This 

 is borne out by the repeatedly verified experiment of removing the 

 ovary from a duck, the result being the assumption of the complete 

 drake plumage at the next moult. Steinach has shown that the 

 implantation of testes in spayed female mammals may bring about 

 the development of secondary male characters, and, conversely, 

 that the implantation of ovaries in a young castrated male (rat or 

 guinea-pig) may induce the apjx^arance of certain feminine char- 

 acters, notably milk-giving mamma\ 



