332 



PARASITISM 



chorion speedily ruptures and the larva issues forth. After a 

 variable period in the mesenteron it bores its way through the gut 

 wall and migrates to the supra-oesophageal ganglion. Within this 

 nerve centre it feeds apparently very little and subsequently 

 escapes into the body-cavity of the host. Here it does most of its 

 active feeding, establishes a respiratory connection with the 

 exterior and completes its development (Fig. 76). Clausen (1931) 

 states that certain Trigonalidse lay their eggs on foliage and they 



Fig. 76. Gonia capitata De G. A, First instar larva on salivary 

 duct of host. B, Unfed larva surrounded by phagocytic cyst 

 (p.c.) ; f.b., fat-body, C, Larva in right lobe of supra-oesophageal 

 ganglion. D, Late larva attached to host-pupa by respiratory 

 funnel (r./.). (After Strickland, loc. cit.) 



are swallowed with the food by caterpillars of saw-flies and of 

 Lepidoptera. The eggs hatch into spinose larvae, which require as 

 their true hosts either Ichneumon or Tachinid larvae. Those 

 Trigonalid larvae which occur in unparasitised caterpillars 

 presumably perish. 



Thompson (1928) has studied the behaviour of the Tachinid, 

 Rhacodineura antiqua, a parasite of the common earwig in England 

 and other parts of Europe. It likewise lays minute eggs (0-13 

 mm. X 0-10 mm.), which are ingested by the earwig and hatch 

 in the mid-intestine. The subsequent history is incomplete, 



