8 INTRODUCTION. 



pupal skin it remains, unlike the Lepidoptera, in the cocoon for 

 a considerable period, during which it attains such perfection 

 both in development and activity that, having gnawed its way to 

 freedom by means of its mandibles, it is capable of flying away 

 quite strongly from the mouth of the orifice, as I have myself 

 observed. 



INTERNAL STRUCTURE. 



The alimentary canal of the imago, as in the larva, is formed, 

 says Newport in describing Trogus, of distinct layers or tissues : a 

 muscular, a glandular, and a mucous ; and is invested externally 

 by a distinct transparent peritoneal membrane, processes or 

 reflexions of which clothe every internal organ, the salivary and 

 hepatic glands, the organs of circulation and reproduction, the 

 adipose tissue and tracheae. The short and narrow oesophagus 

 becomes considerably elongated, and, instead of terminating as in 

 the larva in the mesothoracic segment, is extended in the imago 

 through the metathoracic into the abdominal segments. It is 

 there dilated into a conical crop, which is separated from the true 

 digestive cavity or stomach by a constriction at its apex and a 

 reflexion inwards of its tissues to form the cardiac valve. This 

 portion of the canal, the chylific ventricle, which occupies nearly 

 the whole interior of the larva, is now restricted to the fifth, 

 sixth, and seventh abdominal segments. It is a powerful muscular 

 structure, somewhat elongate-oval in shape and is followed by the 

 excretory or Malpighian organs, from twenty to thirty in number, 

 where, by the internal reflexion of the tissues, is formed a second 

 valve, the pylorus. The canal then becomes narrowed into what 

 may be regarded as the duodenum and ileum, or small intestine. 

 Beyond this it is again dilated into a more muscular structure, 

 the colon or rectum, which terminates at the anal valve. 



EXTERNAL STRUCTURE. 



There are always present a distinctly separated head (bearing a 

 pair of elongate antennas), thorax and abdomen, three pairs of 

 legs, and usually two pairs of membranous wings. 



The head, viewed from above, is transverse or quadrate ; from 

 in front, it becomes more or less strongly narrowed towards the 

 mouth and is always sculptured with punctures or reticulations. 

 The eyes are very large and occupy nearly the whole anterior side 

 of the head. The vertex bears three ocelli, situated triangularly, 

 and behind them is the occiput sloping to the collar. Between 

 the ocelli and the insertion of the antennae is the frons, usually 

 hearing glabrous scrobes upon its anterior portion ; below these is 

 the face, the central portion of which is known as the epistoma, 

 its apical margin being usually separated from the clypeus, which 

 extends across the whole front of the head, by a transverse iin- 



