INNERVATION OF THE GENERATIVE ORGANS 575 



at the periods at which menstruation would occur if the condition 

 were not one of pregnancy. Thus Tyler Smith says that there is in 

 all women a greater tendency to abort at the times represented by 

 the catamenial periods. According to Minot, the menstrual and 

 gravitidal changes follow the same cycle of events, the pregnant 

 uterus passing through a prolonged and intensified " menstrual cycle." 

 Consequently, it is probable that there is a common cause for the 

 ending of the series (the casting off of the superficial part of the 

 mucosa in both cases). This theory has been further elaborated by 

 Beard, who has arrived at the conclusion that parturition takes place 

 at the time it does in order that a new ovulation may be carried into 

 effect. This author lays great stress upon the rhythmical character 

 of the sexual processes, and points out in support of his theory that 

 "heat" and ovulation frequently ensue shortly after parturition. 

 That this does not happen in many animals has been already shown 

 in the second chapter of this work.^ 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, like all other natural 

 phenonema 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 life. 



(10) Eden,^ and also Williams, have pointed out "that the 

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



1 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. 



2 Geyl, " Ueber die Ursache des Geburtseintrittes," Arc'h. f. Gynak., 

 vol. xvii., 1881. 



3 Eden, " A Study of the Human Placenta," Jow. of Path, and Bacterial., 

 vol. iv., 1897. 



