15 



Larval Legs. 



By Alfred Sich, F.E.S. Read April 2'^th, igio. 



The organs of locomotion usually possessed by a lepidopterous 

 larva are three pairs of thoracic legs, which, being the true legs of 

 the insect, develop subsequently into the legs of the imago. 'Fhen 

 there are four pairs of ventral prolegs and one pair of anal claspers. 

 These, being of no use to the insect after the larval stage is over, are 

 absent in the imago, though the scar-like marks of some of these 

 processes are generally traceable on the ventral surface of the pupa. 

 The ventral prolegs and the anal claspers are furnished at the apex 

 with a more or less complete circle of small hooks called crotchets. 

 Dr. Chapman has pointed out that the Obtectae have a series of 

 these crotchets on the inner side of the prolegs only, and the Incom- 

 pletas an entire circle, so that we may take the former type as 

 belonging generally to the Macrolepidoptera and the latter to the 

 Microlepidoptera. The crotchets on the anal claspers are usually 

 arranged in a horse-shoe fashion with the open end of the shoe at 

 the posterior end of the claspers. In attempting more or less 

 successfully to rear Lepidoptera from the egg, I have had some 

 opportunities of noting how and at what stage of larval development 

 these legs and prolegs occur in various types of larvae. In the Nepti- 

 culids the larva, when newly hatched, has no legs at all, but on the 

 venter of the meso- and metathorax there is a slightly raised ridge 

 running transversely across the segment. In the second instar these 

 two segments have each a pair of pad-like processes which are 

 really not connected by a ridge, while in the fourth instar these 

 pads are much larger, and each is furnished beneath, on the sole, 

 with a transverse row of three tubercles, each with a long seta 

 directed backwards. These setaa must materially aid in preventing 

 the larva from stepping backwards. The prothorax has no pad at 

 all, and I believe the reason is that if it had it would come in the 

 way of the larva when thrusting out its head while feeding. In this 

 fourth and last instar the larva also possesses at least six pairs of 

 primitive prolegs, the extra pairs being on the second and seventh 

 abdominal segments respectively. It is a question whether the first 

 abdominal is or is not furnished with prolegs. My own opinion is 

 that it does carry a pair, but that these are much less developed than 

 the others, and are not used in progression. It may be that the 

 ancestral Nepticulid had the pair in question as large as the others, 

 but that the pad on the metathorax increasing in size did most of 

 the work of these two segments, and that now, for want of use, the 



