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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



95 



in one or several somites near the posterior end of the body (fig. 2 A, 

 Grm). The dorsal parts of the coelomic sacs of these segments (figs. 

 2 B, 3 A, a) become constricted from the lateral parts (b) forming 

 a series of gonadial pockets containing the germ cells. At a cor- 



Grm 



Fig. 2. — Diagrams showing the development of the gonads, gonoducts, and 

 nephridia of Onychophora from coelomic sacs and coelomoducts (based on 

 Kennel, 1888, Sedgwick, 1885, Evans, 1902). 



A, cross-section of body segment at theoretical phylogenetic stage represented 

 by embryo with complete coelomic sacs (Coel) and coelomoducts (d), germaria 

 (Grm) dorsal in splanchnic walls of coelomic sacs, gametes (Sps) discharged 

 through coelomoducts. B, later stage with gonadial pouches (a) constricted 

 from lateral compartments (b) of coelomic sacs. C, still later stage, gonadial 

 pouches (B, a) converted into gonadial sacs (G), lateral coelomic compartments 

 (b) connected with coelomoducts, which have become nephridia (Nph). D, ma- 

 ture condition, gonads (G) a pair of dorsal tubes, lateral coelomic compartments 

 (b) reduced to small end-sacs of nephridia. E, longitudinal section, showing 

 gonad connected with lateral gonoduct (Gdl) formed of reduced coelomic sac of 

 penultimate somite, which has maintained its continuity and has not been con- 

 verted into a nephridium. 



a, dorsal pouch of coelomic sac ; AlCnl, alimentary canal ; An, anus ; b, lateral 

 compartment of coelomic sac; BC, definitive body cavity; c, ventral diverticulum 

 of coelomic sac; Coel, coelomic sac; Cpr, coelomopore; d, ectodermal part of 

 coelomoduct; DV, dorsal blood vessel; G, gonad; Gdl, lateral gonoduct; Grm, 

 germarium ; Msd, mesoderm ; NC, nerve cord ; Nph, nephridium ; Spz, sperma- 

 tozoa; VO, ventral organ of ectoderm. 



responding phylogenetic stage, it is to be presumed, the gametes (fig. 

 2 A, B, Spz) were liberated into the coelomic sacs and discharged 

 through the open coelomoducts (c, d) of the latter. In the develop- 

 ing embryo, however, the gonadial pockets are soon shut off entirely 

 from the rest of the coelome (C), and those of each side unite with 



