NO. 14 



INSECT ABDOMEN SNODGRASS 



31 



mental position as the jiaired gonopores of Xiphosurida ; but the posi- 

 tion of the opening is variable with respect to the ventral plate of the 

 genital segment, since it is sometimes behind and sometimes before 

 the genital sternum. The arachnid genital aperture is a gonotreme 

 (fig. 4 G-J, Gtr), inasmuch as it is the immediate opening of an 



Fk;. II.— Pedipalpida and Solpugida : body segmentation and external genitali 



A, Mastigoproctus gigantcus, ventral view. B, Tarantula palmata (Ambly- 

 pygi), base of abdomen of male, ventral surface, with end of genital organ pro- 

 jecting from genital chamber (from Borner, 1904). C, Tarantula juscimanns, 

 male genital organ, dorsal view, exposed by partial removal of walls of genital 

 chamber (from Borner, 1904). D, a solpugid, last prosomal segment and base 

 of opisthosoma with genital opening, ventral view (sex undetermined). 



a, b, walls of genital chamber ; An, anus ; c, genital ducts ; d, spatulate appen- 

 dages of last legs ; Fl, flagellum ; GO, genital organ ; Gtr, gonotreme ; 1L-4L, 

 legs; Pdp, pedipalp; Sp, respiratory apertures; I'l-XVIII, postoral somites. 



ectodermal genital chamber (GC) that contains the true gonopores or 

 gonopore {Gpr). 



The gonads of the Arachnida lie in the opisthosoma. in some cases 

 above the alimentary canal, in others below^ it. Each organ in its 

 fundamental structure is a mesodermal tube containing the germinal 

 cells in its epithelial walls, and is continued anteriorly into a cor- 



