140 THE HUMAN SPECIES 



one single papilla, very broad and smooth, discharges the urine 

 into the pelvis. Whether similar conditions obtain in the other 

 anthropoids has not been ascertained up to the present. 



Reproductive System. 



In a comparison of the reproductive organs of man and the 

 animals it would be a mistake to ignore the non-sexual mode 

 of reproduction which prevails among many animals, from the 

 Protozoa to the Annelida and Arthropoda, for the same pro- 

 cess of segmentation in the cell, which precedes the asexual 

 budding, or gemmiparity, takes place also in the gradual matur- 

 ing of the human ova and spermatic cells. Of far greater 

 significance certainly are the points of contact between man 

 and the animals when we come to sexual reproduction, or 

 reproduction based on differentiation of the sexes, which, 

 commencing in the Infusoria and Sponges, continues throughout 

 all classes of animals up to man. 



In the Sponges, ova and spermatic cells are produced from 

 the parenchymal cells without the mediation of special re- 

 productive organs ; in the Infusoria, the nucleus acts as the 

 female, the nucleolus as the male element, which combine after 

 the conjugation of two individuals. 



In the Ccelenterata, which are either bisexual or of distinct 

 sexes, special organs for the production of generative matter 

 appear only at fixed periods ; when the germinal glands are 

 situated on the surface the generative substance immediately 

 reaches the exterior, but is discharged through the gastro- 

 vascular system when the glands are more deeply situated. 



In the Echinodermata, with the exception of the Synapta, 

 the sexes are distinct, and the reproductive organs are radially 

 arranged. In the absence of sexual organs, the ova are fertilised 

 in the water by the round-headed spermatozoa. 



Of considerably higher organisation are the worms : the 

 hermaphrodite Bryozoa, Turbellaria, Trematoda, Cestoda, 

 Hirudinea and Tunicata. The testicles, varying in number, and 

 the ovary, together'with its vitelline cavity, are generally united 

 at a common opening ; there is also a vas deferens, a kind of 

 vesicula seminalis, and sometimes at the common excretory 

 duct of the ovary and vitelline cavity an expansion appears 



