582 HEKBEKT M. EVANS 



luteum. The French investigators have argued clearly that these pre- 

 gravid changes are only referable to the ovarian lutein bodies, for the 

 formation of the latter constitutes the only new factor introduced in their 

 experiment. The changes are not due to the eggs because these are 

 unfertilized and soon die, nor are fetal membranes responsible, for these 

 are not formed. Furthermore, nervous or other influences resulting from 

 the act of cohabitation itself cannot be responsible, for the production of 

 corpora by mechanical rupture of follicles leads to the same effect. Keller 

 has similarly described a regular postovulatory uterine hyperplasia in 

 the bitch and Corner in the cow. In the rat, as Long and I have shown, 

 the corpora lutea, when mating is prevented, are so shortlived that marked 

 effects on the structure of the reproductive tube are not produced. Mechan- 

 ical stimulation of the lower part of the rats' cervical canal, however, a 

 thing which takes place normally in coitus, in some way produces condi- 

 tions which prolong the functional life of the corpora lutea and when this 

 is the case the latter are able to exert endocrin effects in the form of out- 

 spoken changes of structure even in the vagina, changes which consist in 

 the exchange of a stratified squamous for a very high stratified cylindrical 

 epithelium identical with that occurring during pregnancy. 



Very definite responses hence occur as a result of the functional ac- 

 tivity of the corpora lutea, responses which may be summarized by their 

 designation as the establishment of a pregravid or pseudopregnant con- 

 dition. This condition is most clearly expressed in the lowest of the 

 mammalia, the marsupials, where very remarkable developments take 

 place. The pouch enlarges and its sweat and sebaceous glands reach a 

 state of development and activity only comparable with that found in 

 pregnant animals. The female starts to clean out her pouch in the same 

 way as dees a pregnant one in preparation for the reception of the young. 

 Coincidently mammary hypertrophy is readily palpable, the enlarged 

 glands even being comparable with those found some time after the birth 

 of young. Nor are there lacking uterine changes. The uterine mucosa 

 is hyperemic and thickened, its glands hypertrophied. So evident is 

 the whole condition that the term pseudopregnancy was first applied to 

 the postovulatory condition found in these creatures by Hill and 

 O'Donohue. 10 However, as already intimated, the same phenomena to a 

 varying extent can be found in higher members of the mammalia. 



There is thus a regular succession of events in cyclic oestrus in the rat 

 and presumably in any of the cyclic spontaneously ovulating mammals. 

 By reason of these events it is possible in the living animal to predict the 

 time at which the egg cell is expelled from its site of formation in the 

 ovary, completes its second maturation division and undertakes its journey 



10 These very remarkable changes have all been confirmed by the researches of 

 Hartman on the opossum, the early embryology of which has been so authoritatively 

 handled by him (personal communication). 



