6 INTRODUCTION. 



the very short slender deflexed and corneous mandibles, of variable 

 shape. Beneath these are concealed the labium and maxillae, 

 with the minute palpi of the latter. These organs are usually of 

 dark coloration, but the whole of the body is pale, exhibiting but 

 few distinctive features, excepting the dilated lateral border, 

 which is discrete throughout its entire length from the main body. 



Within the egg the larva is gradually developed 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. 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 endoderrn becomes 

 transformed 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 ileum are gradually evolved from without inwards 

 from a column of cells, surrounded by muscular tissue, connecting 

 the digestive cavity with the anus; their function being to 

 transmit the faeces, they are not perfected till a late period of the 

 larval existence. 



The head and mandibles of the larva, as stated by George 

 Newport in the case of Troyus, are corneous and yellow, with the 

 margins and apices of the latter black. The mandibles are curved 

 and apically acute, fitted for penetration and suction, but not for 

 manducation. The maxillae are three-jointed, with the apical 

 joint broad, triangular, soft, and membranous, the second very 

 short, and the basal joint, both strong and elongate. The labium 

 is triangular, with a slight central ridge. The antennae are 

 entirely rudimentary, but they are represented by small corneous 

 callosities on the frons. The segments are all laterally explanate 

 and project in the form of tubercles, which are especially promi- 

 nent on the three thoracic segments and the basal ones of the 

 abdomen. Their tubercular form is, however, most marked on 

 the fifth and eleventh segments, which also bear distinct mammi- 

 form tubercles laterally upon the venter, acting as locomotive 

 organs. In the later stages of growth these organs approximate 

 more closely, and well illustrate the greater development of the 

 dorsal than of the ventral surface. True legs are indicated only by 

 six points upon the lower surface of the thoracic segments, in the 

 same position relatively as the abdominal tubercles. The propedal 

 process of the apical segment is acuminate and projecting, and is 

 said by Berthoumieu to be reduced to normal form after the 

 second or third moult. It is opposable to another beneath the 

 thirteenth segment, and, with it, forms a prehensile organ, by 



