GENERA L OR GA XOLOGY. 



143 



True Hermaphroditism. With extreme rarity true 

 hermaphroditism (the presence of both kinds of sexual 

 glands in the same animal) has been observed in mammals 

 and in man. What is described as hermaphroditism does 

 not, in the majority of cases, deserve the name. 



Outlets. Very frequently in the animal kingdom the 

 excretory apparatus furnishes outlets for the sexual prod- 

 ucts. In the annelids some segmental organs, in the verte- 

 brates portions of the kidney system, either exclusively or in 

 addition to their excretory function, 

 become accessory sexual organs. 

 Hence we speak of a " urino-gcnital 

 system." This remarkable connection 

 of genital and excretory organs has 

 a double cause, a physiological and an 

 anatomical. Physiologically important 

 is the fact that eggs and spermatozoa 

 behave like excreta ; being substances 

 which are no longer destined for the use 

 of the individual, but must reach the 

 exterior in order to become efficient. 

 The anatomical cause is the relation 

 to the body-cavity; i.e., it is always 

 the case that a urino-genital system 

 is formed only in animals in which 

 the germinal epithelium arises from 

 the epithelium of the body-cavity, 

 and in which the kidneys, or their 

 rudiments, stand permanently, in con- 

 nection with the body-cavity and 

 thus form the natural outlet for its products. Whether 

 the accessory sexual parts are portions of the excretory 

 organs or are independent structures, they have in the 

 animal series a definite arrangement conditioned by their 

 function (Fig. /o). Canals lead from the sexual glands 

 to the exterior, the oviducts in the female, the vasa de- 

 ferentia in the male (and the hermaphroditic duct from the 

 hermaphroditic gland). Oviduct and vas deferens may be 



FIG. 70. Sexual apparatus of 

 Vorte.r viridis ( From Ge- 

 genbaur,afterM. Schultze.) 

 t, testicle ; vd, vasa deler- 

 entia ; vs, vesicula semina- 

 lis ;/, penis ; a, ovary with 

 oviduct ; , uterus ; v, 

 vagina ; rs, receptaculum 

 seminis; gv, yolk-glands. 



