82 WALTER HEAPE. 



it will, I believe, be found that the regularly recurrent 

 dioostrous cycles of the Primates are strictly homologous with 

 the more or less regular dioestrous and ancestrous cycles of 

 the lower animals. 



The Sexual Season in Monkeys. — The consideration 

 of this subject iutroduces a further complication, and that is, 

 while monkeys may have a continuous series of dioestrous 

 cycles, they are not all of them fitted for reproduction at all 

 times of the year. 



Some monkeys in tropical countries may be in a condition 

 to become pregnant at all times of the year ; though this is by 

 no means certain it is not an impossible fact, but others are 

 certainly not so. For instance the chimpanzee and gorilla 

 are said to have a special sexual season in West Africa 

 (Garner, 1896). 



Semnopithecus entellus, from the jungles on the south 

 bank of the Hugli, has a definite time for reproduction 

 (Heape, 1894); and Macacus rhesus, the area of whose 

 geographical distribution is very large, apparently produces 

 young at different and definite times in different districts 

 (Heape, 1897). 



There is every reason to believe, however, that these ani- 

 mals experience regular recurrent dioestrous cycles through- 

 out the whole year. 



If the dioestrous cycle of a monkey is homologous with the 

 ancestrous cycle of a dog — and that this homology exists will 

 be apparent when the question is considered from a histo- 

 logical point of view — it is obvious that we are naturally led 

 to suppose that an increased number of oestri should result 

 in an increased number of opportunities for pregnancy, pre- 

 cisely as in the case of the mare, deer, etc. But this is not 

 so, and the result is that there exist certain mammals which, 

 while they exhibit a continuous recurrence of the dioestrous 

 cycle, have a circumscribed season for conception. 



As I have shown elsewhere (Heape, 1894, 1897), this resulb 

 is due to the fact that, although menstruation recurs I'egu- 

 lai'ly, ovulation does not; or, in other words, that ovula- 



