NO. 14 



INSECT ABDOMEN— SNODGRASS 



germarial area in its wall, of which there is no specific evidence. The 

 erroneous idea that arthropod gonoducts are modified nephridia is 

 probably in part a result of the different significance of the term 

 " gonad " as used by students of Annelida and Arthropoda, but it is 

 largely based on a failure to recognize the essential difference between 



Gdc 



c 



Amp 2Gp NC 2Gp 



Fig. 3. — Development of the genital ducts in Onycjiophora and Chilopoda. 

 (A, B from Kennel, 1888; C from Evans, 1902; D from Heymons, 1901.) 



A, cross-section of a pregenital segment of Pcripatus, diagrammatic, showing 

 subdivision of the coelomic sacs and beginning of formation of coelomoducts 

 {c, d). B, same through genital segment, showing formation of genital ducts 

 from coelomic sacs and coelomoducts. C, section of genital segment of Eoperi- 

 patus wcldoni with ectodermal gonoductus communis (Gdc) giving outlet to 

 the lateral ducts. D, diagrammatic cross-section of genital segment of Scolo- 

 pcndra with coelomic sacs that will become genital ducts. 



a, dorsal compartment of coelomic sac ; AlCnl, alimentary canal ; Amp, 

 ampulla of coelomic sac in rudimentary gonopod ; b, lateral compartment of 

 coelomic sac ; c, ventral diverticulum of coelomic sac ; Coel, coelomic sac ; d, 

 ectodermal coelomoduct ; DV , dorsal blood vessel; Gdc, gonoductus communis; 

 Gdl, gonoductus lateralis; Gp, rudiment of gonopod; mcl, muscle; NC, nerve 

 cord ; Red, rectum. 



an annelid nephridium and the organs given the same name in 

 Onychophora and Crustacea. As shown by Goodrich (1895, 1897- 

 1900), the nephridia and gonoducts of Annelida are probably distinct 

 and separate structures in their origin ; in the Polychaeta the genital 

 ducts in most cases are either united with the nephridia or are reduced 

 to ciliated lobes of the coelomic walls, in which case the nephridia may 

 serve as genital outlets. In the Onychophora and Arthropoda, on the 



