The Larval Head 



27 



The hooks and spines no doubt aid the larva to gras]) 

 firmly with the mouth, as it continually does, not only 

 in feeding, but in creeping ; we have also thought it 

 possible that some of these curious hooks may be used to 

 guide the threads of silk as the}^ are paid out from the 

 salivary duct ^. The lateral {e])icran\al) plates bear two 

 pairs of rudimentary eyes (which are mere pigment-spots 

 without lenses), as well as the antennae and the jaws. 

 The epicranial plates curve round to the under-side of the 

 head, and meet along the middle line in a faintly marked 

 suture, along which 

 the head splits at times 

 of moult. In insects 

 whose head is capable 

 of considerable retrac- 

 tion into the thorax, 

 there may be no 

 suture here, but a wide 

 gap (many Dipterous 

 larvae) ; where the 

 mouth-parts are large, 

 they may almost com- 

 pletely fill the gap, or a separate piece {suhmentiim or 

 gida) may defend the space (Orthoptera, Coleoptera). 

 The fusion of the epicranial plates on the lower surface 

 of the head of the Chironomus-larva is well suited to an 

 insect whose head is small, exposed, and furnished with 

 minute mouth-parts. The genae, which in the cockroacli 

 and many other insects lie along the sides of the clypeus 

 and bear the mandibles, are hardly separable in the 

 Chironomus-larva. 



The larval antennae are small ; each consists of a com- 

 paratively long basal joint, on which is a small, circular, 



' The mouth of the tadpole is armed with rows of liorny teeth, which 

 are not very unlike those of a Chironomus-larva. 



Fi(_;. i6.- 



-Under surface of labrum of larva, 

 with its armature. 



