34G 



INSECTA. 



abdominal segment into the eighth 



rudiment then consists of a cell-strand lying on each side in the 

 dorsal wall of the primitive segments, and extending from the second 



Not only genital cells take 

 part in the formation of this 

 strand, but undifferentiated 

 mesoderm-cells (Fig. 169 B, 

 G) are added ; these originate 

 in the dorsal wall of the 

 coelomic sacs, and become 

 closely applied to and in part 

 surround the genital cells. 

 These mesoderm-cells form the 

 epithelial cells (ep) of the 

 genital rudiment, while others 

 compose a cell-strand (cz) lying 

 medianly and ventrally to the 

 genital cells. 



The genital cells in the 

 female give rise solely to the 

 egg-cells (and to the nutritive 

 cells, in those forms in which 

 these occur). The follicular 

 epithelium of the oviducts, 

 on the contrary, as well as 

 a corresponding cell-layer of 

 the terminal chamber are 

 yielded by the mesodermal 

 epithelial cells.* Phyllodro- 

 7nia, to which the above 

 description refers, and the 

 Orthoptera generally, show in 

 this respect a somewhat simple 

 condition, the germ- or ter- 

 minal chamber of the ovary 

 consisting in them of com- 

 paratively few cells. In most 

 other Insecta, and especially 

 in those which have a great 



* [Each ovarian tube in the adult Insect consists of three parts : (1) the ter- 

 minal filament, (2) a terminal chamber, often serving as a nutritive chamber, 

 and (3) the actual ovarian tube divided into chambers, each containing an ovum ; 

 this last segment is much the longest. — Ed.] 



Fig. 172.— Transverse section through the ab- 

 dominal region of an embryo of 1'hyllodromia 

 germaniea, after the circumcrescence of the yolk 

 and the formation of the dorsal surface are com- 

 pleted, bg, ventral ganglionic chain ; cz, rudi- 

 ment of the efferent genital duct ; d, food-yolk ; 

 r/, terminal filament ; en, entoderm ; fk, tissue 

 of the fat-body; gz, genital cells; h, heart; 

 ps, pericardial septum ; s, tracheal stigma ; sp, 

 splanchnic mesoderm ; vm, ventral longitudinal 

 muscle. 



