174 INTERNAL SECRETIONS OF THE OVARY 



ovulation depends both on the species of animal in question, and 

 also upon the occurrences which take place in the accessory 

 organs. In the short five-day cycle of the unmated rat and 

 mouse it may be asserted that the corpus luteum performs no 

 function. After sterile copulation, however, in these animals, 

 the corpora lutea, now the corpora lutea of pseudo-pregnancy, 

 undergo a greater development and the postponement of the 

 next oestrous period for about twelve days is correlated with the 

 development of other luteal functions during this pseudo- 

 pregnant period. Both the rat and the ntouse, for instance, 

 develop sensitivity of the uterus. This is characteristic of the 

 activity of the corpus luteum and is always found in the 

 normal cycle in the guinea-pig, and also during lactation in the 

 rat and the mouse. In the guinea-pig a prominent luteal phase 

 corresponding to the pseudo-pregnant period in the rat and 

 the mouse occurs in the ordinary unmated cycle. In the 

 Eutheria, the corpora lutea attain their maximum growth and 

 their full functional activity during pregnancy. 



In the rat and mouse, therefore, the history of the corpus 

 luteum of ovulation depends upon (a) whether copulation has 

 taken place, and (b) whether copulation is fertile and 

 followed by the implantation of embryos. In the rabbit and 

 ferret, no corpora lutea are found until copulation has taken 

 place; the corpora lutea then undergo great development, 

 resulting in a period of pseudo-pregnancy which is much more 

 obvious than that in the guinea-pig, rat, or mouse. In the dog, 

 where ovulation is spontaneous at oestrus, a well-marked 

 development of the corpus luteum also takes place quite 

 irrespective of pregnancy, and a definite pseudo-pregnant 

 period is found. There exists, therefore, a reciprocal co-ordina- 

 tion between the accessory organs and the corpora lutea. In 

 the rat and mouse the corpus luteum of ovulation needs the 

 stimulus provided by the act of copulation before it can develop 

 to a functional stage. Further, as in all higher mammals, it 

 requires the stimulus provided by implantation of embryos 

 before developing to the fully mature state. Following parturi- 

 tion in the rat and mouse, lactation causes the corpora lutea of 

 the post-partum ovulation to become persistent for a period of 

 about three weeks. The nature of the stimulus exerted by 



