218 



UASTKOPODA. 



genital organs is far simpler than in the hermaphrodite Pulmonates- 



which have repeatedly been studied but are far from being fully 

 understood, and we shall therefore consider Paludina first. The 

 first rudiment of the genital organs here appears at a time when the 

 velum is still present, and the primitive kidney at its highest de- 

 velopment, i.ff.j somewhat at the stage of Fig. '.Ml. The male and 

 female genital rudiments are similar. 



The germ-gland arises as a rounded outgrowth of the pericardia] 

 sac near the rudiment of the (original) left kidney (Fig. 101, </). which, 



n. — — 



\vr. 



FIG. 101. Transverse section through the posterior end of an embryo of Pal udi aa 

 uiwpwra in the stage depicted in Fig. »9 (after v. Erlanger). ag, efferent genital 

 duct; d, intestine; g, rudiment of the genital gland; I, liver; vies, mesodermal 

 tissue; ink, mautle-cavity ; n, kidney: oe, reno-pericardial pore; ye, pericardium :. 

 //c, ureter. 



as has been stated, degenerates. This outgrowth becomes separated 

 from the pericardial sac as a spherical vesicle which approaches the 

 efferent genital duct (ay) that has now also appeared as a rudiment. 

 The latter arises as an ectodermal invagination from the mantle- 

 cavity, and, according to v. Eblangek, it is very probable that the 

 duct of the (original) left kidney changes direct into the genital duet. 

 It grows out further (Fig. 102, ag) and becomes united with the 

 vesicular rudiment of the germ-gland (Fig. 100, y and ya). The 

 genital gland and its efferent duct now increase considerably in length 



