TRACHEATA. 



419 



epiblast which is invaginated to form the proctodaeum, and in front is pro- 

 longed on each side into two procephalic lobes, in which there are also 

 thickenings of the epiblast (gsae), which become converted into supra- 

 cesophageal ganglia, and possibly other parts. 



Towards the close of the second larval period the muscles (/;;/) become 

 segmentally arranged, and give indications of the segmentation which 



E 



FlG. 191. A SERIES OF STAGES IN THE DEVELOPMENT OF PLATYGASTER. 

 (From Lubbock ; after Ganin.) 



A. B. C. Cyclops larvae of three species of Platygaster. 



D. Second larval stage. E. Third larval stage. 



mo. mouth ; a. antenna ; kf. hooked feet ; Ifg. lateral feet ; f. branches of tail ; 

 nl. lower lip ; slkf. oesophagus ; gsae. supra-cesophageal ganglion ; bsm. ventral epi- 

 blastic plate ; Im. lateral muscles (the letters also point in D to the salivary glands) ; 

 gh. proctodaeum ; ga. generative organs ; md. mandibles ; ag. ducts of salivary glands ; 

 sf. (in E) salivary glands ; mis. stomach ; ed. intestine ; ew. rectum ; ao. anus ; 

 tr. tracheae ; fk. fat body. 



becomes apparent in the third larval period. The third and last larval 

 stage (fig. 191 E) of Platygaster, during which it still remains in the tissues 

 of its host, presents no very peculiar features. The passage from the second 

 to the third form is accompanied by an ecdysis. 



Remarkable as are the larvae just described, there can I think be 

 no reason, considering their parasitic habits, for regarding them as ancestral. 



27 2 



