GENERAL ORGANOLOGY 



107 



mon canal leading to the exterior (ureter) they are commonly aggregated 

 into a compact mass, the 'kidney.' 



B. Sexual Organs. 



Sexual Glands and Ducts. In the sexual apparatus are distinguished 

 the areas where the germ cells are produced, the sexual glands or gonads, 

 and the ducts for these. The former are present, temporarily or perma- 

 nently, in all multicellular animals; the latter may he absent. If the 

 sexual products arise in the skin or in the walls of the digestive tract, as is 

 usual in the ccelenterates, then special outlets are superfluous, since the 

 ripe elements can reach the exterior directly by rupture of their covering 

 or by means of the digestive tract. 



Germinal Epithelium and Germinal Glands. Male and female 

 sexual cells, as we have seen, originate from an undifferentiated incipient 



FlG. 73. Sexual organs of Lnmbricu<; agricala (from Lang, after Yogt and 

 Yung). The seminal vesicles of the right side are removed, but, ventral nerve 

 cord; bv and bl, ventral and lateral ro\vs of sets; st, recepUcula semi n is, ,s/>, seminal 

 vesicles of the left side, connected with a median unpaired seminal capsule (v/>;<). 

 Enclosed in the latter are the te?tes (/;), and the seminal funnels (/), which lead into 

 the vas deferens (rd); o, ovaries; -w, ciliated funnels leading to oviducts with egg 

 capsule ((); di, dissepiments; 8-15, eighth to fifteeeth segment-. 



organ, or anlage, which is called the germinal epithelium. Usually it forms 

 a part of the epithelial lining of the body cavity, in many animals per- 

 manently, in others only temporarily; in the former case it separates, 

 usually by constriction, and forms gland-like bodies, the gonads or sexual 

 glands. 



Gonochorisrn and Hermaphroditism. In n^ost animals the ger- 

 minal epithelium produces either only female or only mak- sexual cells; 



