Il6 WHEELER. [Vol. VIII. 



The primitive germ-cells, which at first occupy only a limited 

 portion of the splanchnic wall, increase in number during a 

 stage midway between F and G. Beautiful caryokinetic 

 figures may then be found in some specimens — showing that 

 the primitive germ-cells themselves proliferate. New germ- 

 cells may be added to the clusters by a differentiation of 

 elements in the splanchnic wall but I have seen nothing to 

 convince me that this occurs. The epithelial cells become 

 much flattened and stain more deeply so that they stand out 

 distinctly among the pale rounded germ-cells which they 

 invest. The inner wall of the somite soon becomes too 

 small to contain all the rapidly accumulating cells and is 

 forced to send out a solid diverticulum. This is directed 

 anteriorly, and in a little later stage fuses with the wall of the 

 antecedent somite. This fusion is probably preceded by the 

 shortening of the embryo which takes place during a stage 

 immediately succeeding Stage F. The result of the fusion is 

 the formation of a continuous strand of germ-cells with their 

 accompanying epithelial cells. For some time the typical hexa- 

 metameric arrangement is still visible in the strand, but later 

 the whole mass shortens very decidedly to form the definitive 

 ovary and testis and all traces of metamerism are lost. In the 

 present paper I shall not follow the development of these 

 organs further, but will pass on to a description of the sexual 

 ducts. This will enable me to supplement the recent work of 

 Heymons ('9l) who has given us an extended and valuable 

 account of the development of the sexual organs in Blatia, but 

 has contributed only a few observations on the development of 

 . the ducts. 



2. The Male DiLcts. 



The sexual ducts like the germ-cells are modified portions 

 of the mesodermal somites. While considering the excep- 

 tional embryo in Fig. 56, attention was directed to the 

 diverticulum {in. d.) of the tenth abdominal somite. This 

 diverticulum, which is quite normal, is destined to form the 

 terminal portion of the deferent duct (spermaduct) and the 

 seminal vesicle of the adult insect. At the base of the divert- 



