61 



(psopliageal ganglion, aud ultimately th.e abdominal 

 ganglia become involved in the meta-thoracic ganglion. 



The germ cells appear at a comparatively late period 

 in development ; they arise a short time previous to the 

 commencement of the formation of the mesenteron. 

 They take their origin from the splanchnic mesoderm in 

 the second and third abdominal segments, and according 

 to Claypole their method of development is as follows: — 

 Those germ cells which ultimately give rise to the male 

 gonads arise from the inner side of the mesoderm, and 

 come to lie free among the yolk (fig. 77). In the case of 

 the female they are budded off from the outer side of the 

 splanchnic mesoderm, and form a group of cells lying free 

 in the mesoblastic somites of those segments. In the 

 case of the male the ccelomic spaces are not formed. In 

 the female the splanchnic mesoderm forms one side of a 

 spacious cavity, which evidently results from a fusion of 

 the contiguous cavities of the mesoblastic somites. The 

 inner wall of this cavity eventually breaks through, and 

 the coelom becomes confluent with the general htemocoelic 

 body-cavity, and at the same time the germ cells come in 

 contact with the yolk. The further development of the 

 werm cells has not been followed in anv detail but, in 

 both sexes, as they develop they incorporate among 

 themselves a large amount of the food yolk distributed in 

 the body-cavity. In newly-hatched individuals much of 

 the yolk is still present in the gonads, and it conduces 

 greatly towards the rapid maturition of the generative 

 elements. 



Of the abdominal appendages, the first pair fuse 

 together and persist in the adult as the ventral tube. 

 The remaining pairs become resorbed, and ultimately 

 completely disappear. 



The eyes and post-antennal organs first become 



