446 



NEUROPTERA 



how many moults they make. The yoimg larva has the head 

 disproportionately large and the branchial filaments longer. 

 AVhen the growth is completed the larva returns to land, seeks a 

 suitable situation in the soil, and after an interval changes to a 

 pupa, in which the characters of the perfect Insect are plainly 

 visible. Su.bsequently, without becoming again active, it changes 

 to the perfect Insect, and enjoys, for a few days only, an aerial life. 

 The anatomy of the larva has been treated by Dufour.^ The 

 supra-oesophageal ganglion is remarkably small ; nothing is said 

 as to the existence of an infra-oesophageal ganglion ; there are 



three thoracic and eight abdominal 

 ganglia ; the first pair of these latter 

 are nearer together than the others, and 

 this is also the case with the last three. 

 The alimentary canal in the adult is 

 provided with a large paunch attached 

 to the crop by a narrow neck,' but 

 Dufour could find no trace of this in 

 the larva. The structure of the bran- 

 chiae has also been described by the 

 indefatigable French entomotomist. A 

 tracheal tube sends a branch into one 

 of the appendages (Kg. 289); the 

 branch gives off numerous smaller 

 tracheae, which at their extremities 

 break up into branchlets close to the 

 integument. The tracheal tube that 

 receives each main branchial trachea, 

 sends off from near the point of entry 

 Structure of tracheal sill of the latter another trachea, that 

 distributes its branchlets on the ali- 

 mentary canal. The margins of each 

 appendage are set with swimming hairs, 

 so that the branchiae act as organs of 

 locomotion as well as of respiration, and by their activity in the 

 former capacity increase the efficiency of their primary function. 

 The genus Sialis occurs in a few species only, throughout the 



1 Anil. Set. Nat. series 3, ix. Zool. 1848, p. 91, pi. 1. 



" Newport, Tr. Linn. Soc. xx. 1851, i)l. 21, fig. 13. Loew, however, who also 

 describes and figures the anatomy of S. lutaria, states that there is no paunch, 

 Linnaea catomolorjica, iii. 1848, p. 354. 



Fig. 289, 



of Sialis lutaria. (After Dufour.) 

 (', Base of the gill ; b, tracheal 

 trunk with which it is con- 

 nected ; c, trachea given off 

 to alimeutary canal. 



