250 Robert, Wilhelm Ilegner. 



the antcecdeiit somite, thus })n)dncing a continuous strand. The 

 hexanietanieric arrangement of the germ-cells disappeared as this 

 strand shortened to form the ovary or testis. Wheeler noted the 

 presence of germ-cells in the first abdominal segment of Blatta 

 germanica in opposition to Ileymon's statement that *'Im ersten 

 Abdominalsegment treten niemals Genitalzellen auf." 



Ileymons' earlier papers were supplemented by a re-examination 

 (1895) of Blatta {Phyllodronila) germanica and a clear account 

 of the develoj)ment of other Orthoptera, Periplaneta orientalis, 

 Gryllus caynpestris, Grylliis domestica and Gryllotalpa vulgaris. 



In Blaita he was able to trace the germ-cells back to an earlier 

 stage than recorded in his former paper (1891). When the poster- 

 ior amniotic fold arose, a groove, ^'Geschlechtsgrube," appeared in 

 the posterior end of the germ-band. Many cells became detached 

 from the bottom of this groove and wandered into the interior; 

 they moved singly and "sicli teils zwischen den Mesodermzellen, 

 teils liber sie hinweg nacli vorn bewegen." They assumed the char- 

 acter of the germ-cells only when they arrived at the visceral walls 

 of the somites where the}' behaved just as previously stated (Iley- 

 mons, 1891). 



In Periplaneta a ''Geschlechtsgrube" also appeared similar to 

 that found in Blatta; cells separated from it and migrated by amoeboid 

 movements toward the anterior abdominal segments where they ar- 

 ranged themselves intersegmentally forming wedge-shaped accumula- 

 tions between the crelomic sacs. Contrary to the condition in Blatta, 

 these could be distinguished as germ-cells shortly after they became 

 detached from the ectoderm. Later these germ-cells separated to 

 form two strands lying on either side of the body in the visceral 

 walls of the second to the seventh abdominal segments ; they acquired 

 an epithelial layer derived from mesoderm-cells. 



A "Geschlechtsgrube" was found by Ileymons (1895) in both 

 Gryllus catnpestris and G. doniesticus, and the germ-cells arose in 

 a manner similar to that in the Orthoptera previously described. 

 These two species differed only in the fact that the germ-cells dif- 

 ferentiated earlier in the former than in the latter. A long oval 

 structure was produced by the accumulation of the primitive germ- 



