710 



CLASS IV. INSECTA. 



eighth abdominal segment is the opening of a bursa copulatrix 

 which communicates internally with the oviduct and which 

 may be enlarged to form a spermatheca. There are also acces- 

 sory glands. The two testes of the male lie in a common capsule ; 

 the vasa deferentia unite to form an ejaculatory duct. The 

 eggs are very varied in colour and sculpture and range from 

 a few dozen to several thousand in number. They may be de- 

 posited promiscuously, or they may be carefully laid on the food- 

 plant of the ensuing larva, which makes its exit after a period 

 varying from a few days to a few months. 



The larva is 

 popularly 

 known as a 

 caterpillar. It 

 has a head 

 followed by 

 three seg- 

 ments the 

 thoracic 

 bearing true 

 legs, and ten 

 abdominal 

 segments, the 



last of which is in some cases difficult to make out. The ab- 

 dominal segments bear a varying number of tubular feet, each 

 ending in a circlet of small hooks, and the body terminates in 

 a somewhat enlarged pair of similar processes. The larva is 

 essentially the feeding stage of the insect, and its stomach is 

 very large. The silk glands are also extensive ; they open by 

 a common duct in the middle of the labium on the spinneret, 

 which is by some homologized with the hypopharynx. Contrary 

 to what obtains in the imago, the mandibles are large and 

 the maxillae and labial palps small. 



The pupa, often termed a chrysalis, reaches its fullest de- 

 velopment in this Order. Its skin hardens and the appendages 

 of the body are glued to the outside. It is incapable of move- 

 ment except for a slight wriggling of the posterior segments. It 

 may be exposed, and has in that case often patches or knobs of 

 a brilliant metallic lustre, or it may be concealed in a cocoon of 

 silk with which some species incorporate extraneous 'materials. 



FIG. 456. Larva of the Poplar Hawk-moth, Smerinthus populi. 

 x 1. A in repose ; B in movement. From Sharp. 



