ENDOPTERYGOTA 427 



The eggs are laid in or near water and the larvae quickly cover 

 themselves with some foreign substances (Fig. 316), building a 

 form of tube from the wide end of which the head projects. Respira- 

 tion is effected by tracheal gills generally found on the abdomen, 

 water currents being passed through the tubular case by the undula- 

 tory movements of the body. The larvae may be herbivorous or 

 carnivorous. Pupation usually takes place within the case after the 

 openings to the case have been closed by silk. The pupa is provided 

 with large mandibles by means of which it releases itself before 

 the emergence of the adult. The free pupa swims to the water's 

 edge by means of its mesothoracic legs and shortly afterwards the 

 adult emerges. Common caddis flies are Phryganea, Limnophilus and 

 Rhyacophila. 



Order LEPIDOPTERA (Butterflies and moths) 



Mouth parts of the imago usually represented only by a sucking 

 proboscis formed by the maxillae; two pairs of membranous wings, 

 clothed with flattened scales, as also is the body; metamorphosis 

 complete ; larvae cruciform with masticating mouth parts, with three 

 pairs of legs on the thorax and often five pairs of prolegs on the 

 abdomen; pupae obtect, either enclosed in a cocoon or an earthen 

 case, or free. 



The imagines live on the nectar of flowers, and to absorb this 

 a highly specialized proboscis has been formed from the greatly 

 elongated galeae of the maxillae, each being grooved along its inner 

 face and locked to its neighbour (Fig. 317). The laciniae are atro- 

 phied and the maxillary palp is usually much reduced. The mandibles 

 are nearly always absent and the labium is represented by a transverse 

 plate and a pair of three-jointed palps. 



Each half of the proboscis is a tube in itself into which passes blood 

 from the head, and also a trachea and a nerve. Across the cavity of 

 this tube there pass a number of diagonal muscles, the contraction of 

 which cause the whole organ to roll up into its characteristic position 

 beneath the head and thorax (Fig. 318). How the proboscis is 

 extended is not fully understood; in all probability, blood pressure 

 plays an important part. 



The length of the proboscis in many cases corresponds to the depth 

 of the corolla of the flower which the species frequents, and in the 

 Sphingidae (hawkmoths) is greater than that of the body. Sometimes 

 the organ is reduced or absent and the animal does not then feed 

 in the adult state at all. 



The beginnings of the proboscis can be traced in primitive forms. 

 In the Micropterygidae there are biting mandibles and maxillae of 



