LATER LARVAL STAGES. 



569 



part along the ventral edge of the protovertebrae where the cutis-lavi-r 

 passes into the skeletogenous layer, small cells filled with deeply 

 staining nuclei can be made out. These are accumulations of primi- 

 tive genital cells which represent the rudiment of the genital gland, 

 and which may perhaps be traced back to HATSCHEK'S large boundary 

 cells mentioned above (Fig. 299, ^, p. 565). These agglomerations of 

 cells are repeated at definite intervals in series of cross-sections. 

 Since they are related to the dissepiments between the rnesodermal 

 somites, they are affected by the asymmetry of those structures and, 

 like them, alternate on the right and left sides of the body. In 

 superficial views of later stages (Fig. 303), the rudiments of the 



FIG. 305. 



FIG. 306. 



FIG. 305 and 306. Later stages of development of the genital rudiment 



in A in /ili i<> ,'n* (after (BovEHi). 



FIG. 307. Genital rudiment in 

 an Aini>/ii<>.i-iiH, 8 nun. long 

 (after BOVERI). 



genital gland can be seen as rounded knobs (gd) lying in small 

 outgrowths in the posterior lower angles of the myocoeles (rudi- 

 ments of the genital pouches). 



Examination of the genital rudiment in the youngest stages reveals 

 that it arises as a modified part of the epithelium on the anterior 

 wall of each myocoele (Fig 304). This epithelial growth then forms 

 a hernia-like invagination into the cavity of the preceding segment 

 (Figs. 305, 306), and in this way constitutes a knob which at first is 

 hollow but is provided later with a lumen (Fig. 307), and which is 

 covered superficially with an epithelium derived from the posterior 

 wall of the segment into which the knob projects, the latter being 



