INTRODUCTION. XXIX 



skin of their victim. The duration of this state has not been observed, 

 but doubtless varies greatly under diverse atmospheric and other conditions. 

 AV'hen the egg-shell splits, the enclosed larva does not at once emerge, but 

 commences to imbibe the juices of its host through the fissure. The larva 

 does not evacuate its shell till after the first moult, its cast skin having 

 been found by Brischke and the older authors attached to the egg. The 

 internal feeder now penetrates the caterpillar's skin and takes up a position 

 between the muscles contained in the splanchnic tissues and the alimentary 

 canal, on the dorsal surface, above the stomach on which it often rests, 

 near the centre of the body and nearly always with its head in the same 

 direction as that of its host. Certain species of Tryphoninae, however, 

 appear to be larviparous, since they may often be seen carrying masses of 

 what Gravenhorst thought to be eggs, but which were proved by Haliday 

 to at least sometimes be living and often cannibalistic larvae, at their anal 

 extremity. In the Pimplinae, &c , the larvae are often external, lying like 

 a muffler round the prothorax of their hosts (usually spiders), while those 

 of certain Cryptinae feed exposedly upon the eggs of spiders, protected by 

 nothing but the thread-sacs which enclose the latter. 



In general, the entomophagous larvae of Ichneumonidae are apodous, 

 soft, whitish or yellowish, nearly cylindrical or ovate, somewhat pointed 

 at each end, and always with a broad lateral border of fleshy tubercles, 

 bearing spiracles. In the earlier stages of growth, and sometimes (as in 

 Orthopelma) throughout it, they are curved. They consist of fourteen 

 segments. The first, or cephalic, segment bears traces of antennae on 

 the frons, below which is a sometimes discreted clypeal area, anteriorly 

 bordered and occasionally reflexed. On either side, below this border, 

 are attached the very short, slender, deflexed and corneous mandibles, of 

 variable shape. Beneath these are concealed the labium and maxillae, 

 with the latter's minute palpi. These organs are usually of dark coloration, 

 as also are the spiracles, but the whole remainder of the body is pale, 

 exhibiting few distinctive features, excepting the explanate lateral border, 

 which is distinctly discreted from the main body. 



Within the egg, the larva is gradually evolved from the ventral surface 

 upwards. Dorsally, the cephalic segments first coalesce, then the anal, 

 and, lastly, the intervening space gradually becomes entire from behind 

 forwards, the prothorax being finally completed. The alimentary canal is 

 also formed from behind forwards. Its anal extremity is the commence- 

 ment of the colon and small intestine, which retain their cellaeform 

 conformation to a late period of the larval life, and constitute, in structure, 

 one of the chief points of distinction between the larvae of parasitic 

 Hymenoptera in general. The digestive apparatus is a hollow cavity, or 

 pear-shaped and elongated sac, with a very short intestine, connecting 

 anteriorly with the short and narrow oesophagus and with the oral organs, 

 though at first closed behind. It is very similar in all hymenopterous 

 parasites, whether internal or external. Its cellaeform, becomes trans- 

 formed into a glandular, structure of two kinds, of which one elaborates 

 the digestive juices, while the other diffuses the results in the form of 

 nutriment throughout the body. In every case the intestinal portions 

 continue small and rudimentary, passing no faeces, till the larva has 

 attained maturity and ceased to feed. The colon and ilium are gradually 

 evolved from without inwards into muscular tissue, from a column of cells 

 connecting the digestive cavity with the anus : their function being to 



