THE FEMALE GENERATIVE ORGANS 543 



this work.i Moreover, Beard's theory makes no attempt to 

 explain why parturition should occur in some animals at the 

 close of one particular ovulation interval (e.g. in the human 

 species at the close of the tenth), and in other animals at the 

 termination of a different one (that is to say, no explanation is 

 given of the variation in the number of ovulation intervals 

 which are comprised in the period of gestation in different 

 animals). It cannot be said, therefore, that Beard's hypothesis 

 as to the time occupied by gestation and the cause of birth is 

 an adequate one. 



(9) Various writers, such as Geyl,^ have laid some stress 

 upon the belief that parturition occurs in women at a time 

 which has proved, after long ages, to be the most suitable for 

 the perpetuation of the race. A similar statement might of 

 course be made about any other existing species of mammal, 

 for it is only another way of stating the generally accepted 

 belief that parturition, Uke all other natural phenomena in the 

 animal world, is under the control of natural selection. In 

 support of this contention, as apphed to the human species, it 

 has been pointed out that when labour takes place after an 

 abnormally prolonged gestation, it frequently results in dead 

 children, while, on the other hand, premature labour results in 

 puny, ill-developed children, who often perish in early hfe. 



(10) Eden,* and also WiUiams, have pointed out " that the 

 frequent occurrence of infarct formation [i.e. a certain kind of 

 degenerative change] in the placenta at term must be regarded 

 as evidence of its seniUty, and that this change is analogous 

 to the obhteration and atrophy of the chorion leeve at an earher 

 period. Where these changes are marked the nutrition of the 

 foetus must be interfered with, and it is possible that certain 

 of its metabohc products may result in stimulation of the 

 uterine centre." * This theory should be compared with that 

 advanced by Spiegelberg (see above). 



^ Beard holds that ovulation takes place shortly after parturition in all 

 Mammals. This is not the case in any monoestrous animals which have a 

 prolonged anoestrous period. 



" Geyl, "Ueber die Ursaohe des Gehurtseintrittes," Arch. f. Oyncih., 

 vol. xvii., 1881. 



' Eden, " A Study of the Human Placenta," Jour, of Path, and Bacieriol., 

 vol. iv., 1897. * Williams, loc. cit. 



