Ryder.] [May 16, 



These processes seem to have grown up as if superimposed upon each 

 other, just as it can be shown that the progress of enibryological onto- 

 genetic development has followed as a consequence of the superimposition 

 of one morphological complication upon the immediately preceding one, 

 and often as a consequence of direct adaptation. Similarly, the inclusion 

 of the germ tracts, as morphological advances shut off the gut-pouches 

 from the archenteron, became more decided. The complexity of the out- 

 lets for the reproductive products, at first by way of the nephridia, as these 

 were fused into a serially connected system, became more marked, the 

 sexual products were now discharged through the passages serving also 

 for the emission of the urinary secretion. Finally, this passage became 

 divided lengthwise, so as to serve for the separate discharge of the urinary 

 and sexual products, until at laat the lower end of the reproductive 

 channel became modified into a brood chamber or uterus for the viviparous 

 development of the young, accompanied with sexual intercourse, now 

 rendered possible by the further modification of the extreme outer por- 

 tions of the reproductive passages and the parts immediately adjacent to 

 them. 



Part passu with the higher development of the reproductive processes the 

 fertility of the female became absolutely reduced, partly in consequence 

 of the precocious overgrowth of the female germs through a primary sup- 

 pression of the tendency to spontaneous segmentation of such germs, as 

 will be more fully illustrated later. This reduction in the fertility of the 

 female gonads is also doubtless correlated with the increased chances of 

 the survival of the offspring produced by the more protective methods of 

 reproduction, while the material diverted from ovogenesis, to carry on the 

 formation of secondary egg- envelopes, incubation, nidification, gestation, 

 placentation, lactation and other parental care, also reacts directly upon 

 fertility, while the great lengthening of the period of fetal and infantile 

 development, tends to still further reduce the possibilities of rapid repro- 

 duction. The recurrence of the seasons tends to make the reproductive 

 periods annual in all forms except the lowest asexual, and the highest 

 form, man, who lives under approximately uniform artificial conditions of 

 his own creating. There is, therefore, a widespread tendency toward a 

 reduction of the fertility of most forms below what it would be if there 

 existed uniformly favorable conditions throughout the year, due solely to 

 the recurrence of unfavorable annual periods. 



The fertility of the male, or rather his functional activity, may be 

 affected in a corresponding manner by the seasons, but the absolute fer- 

 tility of the male as compared to the number of germs produced is 

 invariably greater than that of the female, usually by many thousand- 

 fold. This greater male fertility depends upon the minute size and rapid 

 production of male elements through the breaking down of protova 

 spermatogonia and the rapid integration of chromatin or nucleoplasm as 

 will be shown later. Such a rapid and abundant production of male 

 elements may be one of the causes leading to the persistent pursuit of the 



