Eyff-burster of Eucephalous Fhj-larvos. 



375 



cflbrti'd by a pair of muscles which are attached to tlie inside 

 ot the disc and pass across to the vcntial side of the head. 

 '1 lu'sc muscles are easily seen iu the perfectly transparent 

 larva of I'haohorus [Corethra) ; they are shown also in the 

 accoMipanyinf? diajjram of the etig-burster of TheobalJia 

 aiinulatu. Thou<>;li they almost meet on the chitinous disc, 

 the muscles are wide apart at tlieir ventral insertion. I have 

 not ascertained Avh(!ther they persist beyond the first larval 

 staue. One must sup[)ose th.it the efj'i;-burster i- r.-iised and 

 so brouiiht into use by blood-pi*essuie on the relaxation of 

 tiiis pair of muscles. 



The precise form of the chitinous disc varies somewhat 

 in the different species examined. It is relatively larger 

 and more conspicuous iu the Culicidie than in the Chirouo- 

 midtu and IMycetophilidaj, while among the Culicidtc it is 



Fig. 4. 



ISimuliuvi nusteni, Edw. 



Dorsal view of head of uewly hatched larva, showinr,' miinite egg-biiister 

 iiear posterior eud of clypeus. x about 60. From a spirit- 

 specimen. 



decidedly more heavily chitinised in Aedes than it is in 

 Tlieohaldin or Anopheles. In Aides it is connected by a 

 narrow chitinous rod witli the posterior part of the ely[)eus, 

 the rod arising from a thickened bar in the chitin. 1 have 

 not been able to detect this rod in other Culicidse or in 

 the other families examined. The eggs of Aedes have 

 usually great powers of resistance to dessication, and pro- 

 bably on this account have a thick chorion, which necessitates 

 a more efficient egg-burster. 



The two species of ^(V/es examined show slight differences ; 

 the egg-burster in A. argenteus is nearer the posterior eud 



J5^ 



