INTRODUCTION 



in Eriocephala developed. Usually there is a spinneret beneath 

 the mouth, from which a fine silk is produced. Segments 2-4 

 bear each a pair of true jointed legs, corresponding to those of 

 the imago, seldom absent. In addition to these there are also 

 in the normal type of Lepidopterous larva ten prolegs, sucker- 

 like extensions, whose extremities are furnished with series of 

 minute hooks, situated in pairs on segments 7-10 and 13, but 

 some or all of these may be rudimentary or absent. In the 

 archaic Eriocephala there are prolegs on 5-12 ; and in one or 

 two other instances there are rudimentary paired ventral pro- 

 cesses on other segments than those on which prolegs normally 

 appear, but so little developed that it can hardly be deter- 

 mined whether they are really homologous with the true pro- 

 legs or not. The surface of the body is furnished with 

 numerous dots, spots, or tubercles (variously styled according 

 to their character, which varies much in different species), of 

 which some at least usually bear each a fine hair, or sometimes 

 dense fascicles of hairs ; sometimes these tubercles are developed 

 into spinous processes, branched with hairs. The spiracles, or 

 orifices of the respiratory tubes, are placed in a row along the 

 sides of the body, not far above the legs. The contractile 

 dorsal vessel, which is the main circulatory organ, runs along 

 the middle of the back, and is often visible through the skin. 



The whole growth of the insect takes place in the larval 

 stage, the increase of bulk being frequently very rapid. 

 During the process the larva casts its skin several times 

 (usually from four to six), sometimes undergoing considerable 

 changes of appearance and habit on these occasions. 



The markings of larvae usually take the form of longitudinal 

 lines ; of these the one which runs up the middle of the back 

 is termed the dorsal, that which includes the spiracles the 

 spiracular line ; those which margin the spiracular are the 

 supraspiracular and subspiracular respectively ; between the 

 dorsal and spiracular are placed two others, the upper being 

 the subdorsal, the lower the lateral. These are seldom all 

 present; the dorsal and spiracular alone rest on a structural 

 basis, the others being assumed by a useful convention. 



Ovum. 



The ovum, or egg, is small and more or less globular ; 

 its surface is frequently sculptured, and assumes special char- 

 acters in particular groups ; the colour usually undergoes 

 marked changes during the development of the embryo. 



