INTERNAL STRUCTURE OF THE BUTTERFLY LARVA. 25 



are usually quite circular, whilst spiracles are ordinarily oval, 

 and they present no opening in the centre, but only a simple 

 pit of more delicate structure than the chitinous annulus itself. 

 They are also found in some Urbicolid larvae in their first stage 

 and sometimes also throughout life, but for the tenuous structure of 

 the pit in the centre, they would have all the appearance of suppressed 

 spines, and, indeed, the central pit seems sometimes to be wanting, and 

 we have simply a shining lenticle, similar to those which are common in 

 the Papiiionids, but whether they should be looked upon as structures 

 on their way to some use, or as effete structures, degenerated spines, 

 so to say, we have no evidence at present to show, and an explanation 

 of their purpose has still to be sought. 



CHAPTER VIII. 



INTERNAL STRUCTURE OF THE BUTTERFLY LARVA. 



The internal anatomy of the butterfly larva is exceedingly complex. 

 The external features of the butterfly larva are comparatively easily de- 

 scribed, and the position of the structures located owing to the segmented 

 form of the body, and the fact that special organs and appendages are re- 

 stricted to certain segments. The dealing with the internal organs and 

 structures, is, however, a much more difficult matter, as most of them are 

 not restricted to certain segments, but run longitudinally through the 

 body, sometimes extending from the thorax, forward into the head, or 

 backward into the abdomen. It is, therefore, necessary to consider 

 each separately, both as regards position and function. The movements 

 of the body are of the first importance, and the larvae have, in various 

 species, undergone great modifications to enable them to vary their 

 movements according to their needs. Movements are dependent on the 

 muscular system, and the changes that take place in the appearance 

 and configuration of the larva, when movement occurs, are due to the 

 muscles. The nutrition of the various parts is maintained by food, 

 and, to comprehend this, the digestive or alimentary system must be 

 studied. The absorption of the digested food into the blood and its 

 carriage to the different parts of the body, necessitate a circulatory 

 system, whilst the oxygenation of the blood leads up to a consideration 

 of the respiratory system. This latter is so intimately connected with 

 the excretion of waste, that one is forced to consider the excretory 

 system, whilst the organs, by which the whole of these various systems 

 is governed, comprise what is known as the nervous system, and this 

 has to be considered, both in its relation to volition and sensation. 

 These various systems comprise, then, the different organs (and their 

 functions) by means of which the life of an insect is carried on, and 

 their external results, as exemplified by their movements, etc., are the 

 outward signs of their vitality. The reproductive system, which is not, 

 however, matured, nor very largely developed, in the larval stage, must 

 take the highest place in relation to the continued life of the species. 

 Closely related, 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. We 



