THE INTERNAL STRUCTURE OF THE LEPlDOPTEROUS LARVA. 55 



too, with the digestive, is the cellular, system, by means of which the 

 caterpillar is able to store up large quantities of surplus material for 

 use in the later stages of its metamorphoses. 



The voluntary muscular system of the caterpillar is that by means 

 of which it is enabled to move about in order to obtain its food. The 

 muscular fibres are usually arranged in the form of flat ribbons, or 

 conical bundles. The latter make up almost the whole structure of 

 the head, are fastened chiefly to the head walls, and end as fine 

 tendinous cords, attached to the various organs which the insect is 

 thus enabled to move. In this way, certain muscles reach down into 

 the mandibles, which they close when they contract ; whilst the 

 mandibles are opened by muscles which are attached to their outer 

 bases and to the head, just below the ocelli. Other fine flat retractor 

 muscles draw the labrum inwards, whilst extensor muscles work in 

 the opposite direction. A series of contiguous muscular cords, often 

 forming a double band of simple, longitudinal muscular fibres, runs 

 from one end of the body to the other, on each side, just under the 

 skin, between the spiracles and the ventral area of the body. Mus- 

 cular bands, too, run transversely and obliquely in the front of each seg- 

 ment, and are attached to the medio-ventral line farther back in the 

 segment. Above the spiracles on each side are other longitudinal 

 bands, made of three layers, whilst between these and the skin, at the 

 front of each segment, a transverse muscular belt encircles the body, 

 passing at the spiracular region over the longitudinal tracheal vessel, 

 which unites the contiguous spiracles, and straps it to the integument. 

 The flexor muscles of the true legs arise just beneath the longitudinal 

 straps, previously described as running between the spiracles and the 

 ventral area, and extend to the opposite wall of the segment in which 

 they take their rise. The muscles of the prolegs are somewhat different, 

 flat bands forming, as it were, a muscular coating to the walls of the 

 legs just beneath the skin. Usually, these pass directly down, narrow- 

 ing as they go ; the muscular fibres, too, appear not to cross to opposite 

 sides of the leg. 



The involuntary muscular system is principally connected with the 

 digestive and the circulatory organs. The oesophagus is provided with 

 fine longitudinal bands of muscular fibres, and also with less well- 

 developed transverse encircling bands. The inner coating of the 

 stomach is enclosed in delicate strips of muscular fibre, crossing each 

 other diagonally; besides these, longitudinal muscles run throughout 

 its length, and well- developed transverse muscles encircle the stomach 

 similarly to those found in the oesophagus. The arrangement of the 

 muscular tissue in the intestine, in longitudinal and transverse bands, 

 is very similar to that in the other parts of the alimentary canal, but, 

 in this, the longitudinal bands are often thick, white and glistening, 

 whilst near where the small intestine joins the stomach, the walls are 

 plentifully supplied with short longitudinal muscles. The diagonal 

 bands found in the stomach have also their representatives here. 



The alimentary canal is held in its place by a series of muscular 

 bands attached to the body wall, one set passing round that portion of 

 the intestine where it is connected with the stomach, another set being 

 attached to, and supporting, the posterior end of the small intestine, 

 these muscles stretching horizontally from the middle of one side of 

 the 8th abdominal segment to the opposite side. 



