MESODERMAL DERIVATIVES 125 



The dorsal plate now separates from the walls of the body cavity, and its 

 flat, elongate cells become arranged in about 20 vertical rows (Fig. 54, tf). 

 These columns of cells form the terminal filaments of the definitive 

 ovarioles. The first appearance of the egg tubes is indicated by a series 

 of dorsal swellings of the middle region corresponding to the columns of 

 filament cells. Then the swelUngs are converted into definitive ovarial 

 lobes by a deepening of the grooves between them, until finally the gonad 

 is cut vertically into separate compartments as far as the ventral strand. 

 The compartments are the ovarial tubes, each of which is covered by an 

 epithelial layer of mesodermal cells and contains a number of egg cells 

 {gc). In the opinion of Snodgrass (1933) this probably represents the 

 primitive condition of the female reproductive organ formation. 



X 



Fig. 55. — Later stage of ovary of Blattella with gonad divided into ovarioles. (d) Duct. 

 (ovt) Ovariole. {tf) Terminal filament, (x) Calyx. {Adapted from Snodgrass.) 



The exit apparatus of the egg tubes is formed from the ventral strand 

 of the gonad, which becomes cleft between the attachments of the tubes 

 upon it and thus divided into the rudiments of the ovariole pedicles 

 (Fig. 55). The undivided part of the ventral strand and its posterior 

 continuation become the lateral oviduct (d), the anterior end of which 

 supporting the pedicles is widened to form the calyx (x). By a shortening 

 of the calyx, the egg tubes of the roach become horizontal, and the 

 ovary assumes its definitive form and position. In many insects, how- 

 ever, as in Ephemerida, Dermaptera, Plecoptera, Phasmidae, and 

 Acrididae, the ovarioles preserve their more primitive serial arrangement 

 on the elongate calyx, as in an immature stage of the cockroach (Fig. 55). 



The development of the testes does not differ materially from that 

 of the ovaries. The sperm tubes usually lack terminal filaments, and 

 the division of each testis into compartments is not always apparent 

 externally and is sometimes incomplete. In Pieris the lumen of the testis 

 is undivided until about the time of hatching, when the formation of the 

 septa begins which will divide the organ into four tubular sections. The 

 septa are infoldings of the testicular wall, which grow inward toward 

 the posterior ventral part of the organ where the duct arises. 



