118 



GENERAL PRINCIPLES OF ZOOLOGY. 



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 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 permanently, in others only temporarily; in the 

 latter case it separates, usually by constriction, and forms gland- 

 like bodies, the gonads or sexual glands. 



Gonochorism and Hermaphroditism. In most animals the 

 germinal epithelium produces either only female or only male 

 sexual cells; such animals are called separate-sexed, dio&cioiis or 



di 



FIG. 71. Sexual organs of Lumbricm agricola. (From Lang, after Vogt and Yung.) 

 The seminal vesicles of the right side are removed, Zwi, ventral nerve- cord; IIP 

 and of, ventral and lateral rows of setae; st 1 , st 2 , receptacula seminis; sb 1 , sb 2 , TO", 

 the three seminal vesicles of the left side, which are connected with a median 

 unpaired seminal capsule (sbw). Enclosed in the latter are the anterior and pos- 

 terior testes (Ti 1 , ft 2 ), and the anterior and posterior seminal funnels (t 1 , t 2 ), which 

 lead into the vas deferens (vd). o, ovaries; to, ciliated funnels leading into the 

 oviducts (ov); di, dissepiments; VIII-XV, eighth to fifteenth segments. 



gonochoristic, in opposition to the hermaphroditic forms, in which 

 both kinds of sexual glands are contained in one and the same 

 individual. Different degrees of hermaphroditism can be distin- 

 guished; commonly testes and ovary are contained in the same 



