THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 33 



species. In some, the apex is chisel-like ; in others, serrated ; in yet 

 others, pointed. Below and behind the mandibles or upper jaws are 

 found the fleshy bases of the maxilla or lower jaws, each of which 

 bears a short fleshy joint, to which the maxillary palpi are attached. 

 The inner palpus consists usually of only one or two joints, and is in- 

 conspicuous ; the outer is more conspicuous, and consists of three joints, 

 of which the two outer are somewhat horny and minute. The under 

 surface of the head, lying between the basal portion of the maxillae, is 

 occupied by the labium or lower lip. The labium bears, near its tip, on 

 each side, a pair of minute two-jointed palpi, which, from their 

 position, are termed the labial palpi ; their basal part is long, and the 

 upper very minute. The apex of the labium is strangely developed 

 into a small horny tube, from a hole in the tip of which the fluid which 

 is secreted, and which ultimately forma silk, is passed, the tube itself 

 being known as the spinneret. In the caterpillar, the antennae are 

 very small and ill-developed. They consist of a pair of four-jointed 

 organs, one on each side of the face, placed just outside the base of 

 the mandibles. The basal joint of the antennae is large and fleshy, 

 the remainder being much more slender, and varying somewhat in 

 shape. The third joint usually carries a long bristle. On each cheek 

 are to be seen the six ocelli, placed just above the base of each antenna ; 

 each one looks like a smooth, hemispherical, protuberant wart, and 

 they vary in colour in different species. Five of them form, usually, 

 a somewhat regular curve, and are placed close together, whilst the 

 sixth lies a little further away, often towards the centre of the cheek. 

 As may be expected, the detailed characters of the head-parts vary 

 somewhat in the different super-families of the Lepidoptera, but the 

 general characters hold good. 



The head, too, varies greatly as regards the clothing and secon- 

 dary organs that it bears. It is usually more or less tuberculated, 

 the tubercles bearing hairs, and there can be no doubt that an actual 

 ontogenetic relationship exists between these and the tubercles of the 

 body segments. The head segment nearest to the thorax, which forms 

 the summit of the head, is sometimes ornamented with long pointed 

 chitinous horns, spiny tubercles, ear-like processes, etc., all of which 

 are prolongations of the corneous head structure. These undergo as 

 varied and as different changes at each exuviation as do those of the 

 body segments, in which simple hair-bearing, warty tubercles become 

 developed into most complicated structures as some larvae approach 

 maturity. 



We have already stated that the head is composed of at least four 

 segments. We are so accustomed to look for organs in all animals 

 having a somewhat similar function to analogous parts in our own 

 body, that it is easy to overlook their real morphological significance. 

 There can be no doubt that in insects the mouth proper is a simple 

 hole, and that the mandibles, maxillae, etc., are simply modified appen- 

 dages on the various segments of which the head is built up. We may 

 see how the modification has been brought about by a careful study of 

 the limbs of a Crustacean (e.g., a crab or lobster). The mouth-parts, 

 it is clear from such an examination, are undoubtedly limbs, modified 

 first to hold, then to break, and lastly to masticate, the prey. Ideally, 

 the head is made of several segments, each bearing a pair of organs — 

 labrum, mandibles, maxillae, labium — which are homologous with 

 the true legs, c 



