INTRODUCTION. XXXI 



apices nearly approximate. The abdomen is fully developed, though the 

 lateral tubercles are still very conspicuous, and the conformation of the 

 basal segment undergoes considerable modification during the pupal state. 

 The genital organs are very prominent, at first rudimentary and surrounded 

 by thick liquid, but gradually becoming perfect as emergence approaches.^ 

 The legs are pressed closely to the sides of the body ; the femora are 

 drawn forward and the tibiae folded back upon them ; the tarsi lie along 

 the outer side of the antennae in a continuous line, the hind ones 

 extending to the base of the seventh ventral segment. 



As is the case in most Hymenoptera, the final quiescent condition of 

 the larva is protracted to the proportionate brevity of its i)upal existence, 

 which often is no longer than of ten days' duration. As far as my observa- 

 tion extends, the mandibles of these insects serve but one purpose, that of 

 effecting an exit from their hosts', or their own, cocoons. May we not, 

 therefore, forecast in some measure from the greater or less development 

 of these organs upon what kind of host they prey, or is it not rather the 

 amount and potency of the potassium hydroxide secreted to aid the 

 mandibles in this function by which we should judge the solidity through 

 which they are capable of forcing their way ? Thus, the mandibles of 

 Pnnisais cephaloies, a parasite upon Dicranura vmuln, are certainly stouter 

 than those of Steuichnetimon trilineatus, which preys upon Abraxas grossu- 

 lariata. After the imago has thrown off the pupal sheath, it remains, 

 unlike the Lepidoptera, in the cocoon for a day or two, during which 

 period it attains such complete perfection that, having effected an exit by 

 means of its mandibles, its wings are already available for flight and nothing 

 retards its instant volition. 



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 trans- 

 parent 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, by a constriction at its apex and a reflexion inwards 

 of its tissues to form the cardiac valve, is separated from the true digestive 

 cavity or stomach. 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 hepatic 

 or Malpighian organs, from twenty to thirty in number, where, internally 

 by 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 ilium, or small intestine. Beyond this it is again dilated into a more 



1 In Paniscus I have noticed these organs not to become perfect initil after the pupa is so far 

 advanced as to be able to move its legs. 



