NO. 6 ANNELIDA, ONYCHOPHORA, AND ARTHROPODA SNODGRASS 75 



the somite of the oral papillae and the somite of the genital ducts 

 become constricted from the ventral parts (fig. 32 C, a), and then 

 separated as independent dorsal compartments (D, a). In the pre- 

 genital somites the dorsal compartments disappear, but in the defini- 

 tive genital somites they persist as gonadial sacs containing the 

 germaria (fig. 34 C, (7). The gonadial sacs of each lateral series, 



Grm 



Grm 



Fig. 34. — Diagrams showing the transformation of the onychophoran coelomic 

 sacs and coelomoducts into genital organs and nephridia. (From Snodgrass, 

 1936, based on Sedgwick, 1885, Kennel, 1888, and Evans, 1902.) 



A, theoretical primitive stage in which excretory products and the gametes 

 were discharged from the coelomic sacs through coelomoducts. B, C, D, differ- 

 entiation and division of the coelomic sacs into dorsal gonadial sacs (a) and 

 ventral nephi*ic sacs (6), the last finally reduced (D) to end-sacs of the 

 nephridia. E, gonadial sacs of definitive genital segments united on each side 

 in a gonadial tube (G) opening through undivided coelomic sac of penultimate 

 somite. 



a, gonadial compartment of primitive coelomic sac ; AlCnl, alimentary canal ; 

 An, anus ; b, nephric compartment of coelomic sac ; BC, definitive body cavity 

 (haemocoele) ; c, nephridial diverticulum of coelomic sac; Coel, coelomic cavity; 

 Cpr, coelomopore; d, ectodermal part of coelomoduct ; DV , dorsal blood vessel; 

 G, gonad ; Gdl, lateral gonoduct ; Gld, accessory genital gland ; Grm, germarium ; 

 Msd, mesoderm; NC, nerve cord; Nph, nephridium; Spz, spermatozoa; VO, 

 ventral "organ" of ectoderm. 



however, unite in a continuous tube (E, G), which becomes the 

 definitive gonad with a germinal band in its ventral wall (C, D, (7). 

 Furthermore, the posterior ends of the gonadial tubes open into the 

 coelomic sacs of the following somite, and these sacs, which maintain 

 their integrity, and their continuity with the coelomoducts (fig. 32 E, 

 a, b, c, d), become the lateral genital ducts (fig. 34 E, Gdl). Eventu- 



