No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 1 23 



unable to detect the presence of germ-cells till the somites 

 were established (Stage a little younger than F). At this time 

 they formed strictly metameric cell-clusters each of which was 

 confined to the median portion of the splanchnic wall of its 

 respective somite. These cells rarely, if ever, strayed into the 

 dissepimental region during this stage. It is, of course, con- 

 ceivable, that XipJiidiinn and Blatta may differ very consider- 

 ably in respect to the point under consideration, but I suspect, 

 nevertheless, that Heymons has mistaken the young vitellophags 

 for sexual-cells, notwithstanding his assertion to the contrary. 

 At any rate, to be complete, his figures should show the vitel- 

 lophags, which are undoubtedly present in the stages he 

 studied and which occupy the very location of his "sexual- 

 cells" in his Figs. 2 and 3. 



Another point on which we differ is the distribution of the 

 germ-cells. According to Heymons they occur in Blatta in 

 the second to seventh abdominal segments, whereas I find 

 them in Xiphidiiim in the first to sixth. Heymons says 

 emphatically: " Im ersten Abdominalsegment treten niemals 

 Genitalzellen auf." But this is certainly an error, for 

 in several Blatta embryos I find unmistakable germ-cells 

 forming a pair of isolated clusters in the first abdominal 

 segment. Here they also persist till a comparatively late 

 stage when they are drawn into the second segment during 

 the contraction of the sexual Anlage. The peculiarly modified 

 pleuropodia in Blatta form so efficient a means for determin- 

 ing the exact position of the first abdominal segment and its 

 somite in series of sections both longitudinal and transverse, 

 that I feel confident of not being mistaken in this matter. I 

 admit, however, that fewer germ-cells occur in the first than in 

 the succeeding abdominal segments. According to Heymons 

 comparatively few germ-cells occur in the seventh pair of 

 abdominal somites. In these I have never seen traces of 

 germ-cells in Xiphidmm but I cannot, of course, assert that 

 they never occur, especially as I have shown that germ-cells 

 may be found even as far back as the tenth segment. It is 

 interesting to note that Heymons, too, found germ-cells in some 

 of the posterior abdominal segments in Blatta. 



