436 Experimental Zoology 



female develops; if the latter, a male. We lack the evidence 

 to establish such a view at present, and our more immediate 

 problem is first to discover what factors determine the sex of 

 the individual. 



So far we have considered only the effects of removal of the 

 essential organs of reproduction, the ovaries and testes, on the 

 general characters. It has been shown for the males that 

 the removal of these organs in youth also affects the acces- 

 sory parts of the reproductive organs, the glands and ducts. If 

 the testes are removed from the adult mammal, there is a decrease 

 in the size of the prostate gland that may be due to functional 

 atrophy, or may be due to more direct influences. If the testes 

 are removed from a young animal, the prostate does not develop 

 further, and remains quite small. One-sided castration pro- 

 duces no effect, either on the same or on the opposite side. The 

 development of Cowper's gland seems to be correlated with the 

 development of the prostate, and after castration remains un- 

 developed. Other parts of the accessory system also fail to 

 develop completely after castration. 



It is generally assumed that the influence arising from the 

 testes must be in the nature of an internal secretion, which, set- 

 ting free certain materials in the blood, affects the development 

 of remote parts of the body. In support of this view is the fact 

 that the influence is not unilateral, but general. There is a 

 further result that shows how important a role the internal secre- 

 tions of the reproductive organs may play in certain changes in 

 other parts of the body. It has been found by Frankel and 

 Cohen that the presence of the cup-shaped corpora lutea, left 

 on the surface of the ovary after the egg has escaped, is necessary 

 for the fixation of the egg to the wall of the uterus. The egg or 

 young embryo fixes itself six days after it has been set free from 

 the ovary. If the ovary is removed at this time, the fixation does 

 not occur. Even if the ovary is left, but the corpora lutea are 

 destroyed by a galvanic needle, the fixation fails to take place. 

 It is probable that the corpus luteum is a gland, as its structure 

 suggests, and the substance produced influences the wall of 



