146 CERURA VINULA. 



tlieir full length before they disappear. During the 

 moult there can be plainly seen an extra tracheal 

 thread from between the third and fourth segments. 

 When the larva is free from the old skin it scrapes off 

 the old headpiece by pulling it against the edge of the 

 leaf on which it is fixed, and then turns round and 

 places itself in position as if to begin at once eating 

 the cast skin ; but this is not done for some hours. 

 As I mentioned before, Dr. Chapman found that the 

 leaf on which the moult took place was also eaten up, 

 and he considered this was done for the sake of the 

 silk spinning on it, which in some way is good for 

 the health of the larva. The full-grown larva is more 

 than 60 mm. long when stretched out, and in that 

 position the head and the hump on the back do not 

 look so large and conspicuous as when the larva is at 

 rest and contracted. The body is stout, with the 

 hinder segments tapering to a point, a transverse 

 dorsal hump on segment 4 ; the tails, 10 mm. long, set 

 with short points ; the face is somewhat flat, the head 

 retractile into segment 2, which thus becomes puffed. 

 On the back of 2 is a sort of shiny plate, slightly pitted, 

 very wide and squared in front, and rounded on the 

 hinder edge ; the anal flap has a plate, and it ends in a 

 small pair of points. Below the anus is another pair of 

 points ; these points receive the pellets of frass and 

 jerk them to a distance. From the tails can be pro- 

 truded two filaments or whips, but as the larva grows 

 large it is not easily excited to do this ; their use has 

 been supposed to be for defence against ichneumons, 

 but I have taken full-fed larvse which had rows of 

 ichneumon eggs fixed on the back and sides in the 

 folds between the anterior segments. Under the mouth, 

 at a distance of 2 mm. from the head in the skin-fold, 

 and about 1 mm. in advance of the front pair of thoracic 

 legs, is a transverse cleft, 3*5 mm. wide, the mouth of a 

 cavity which contains a quantity of clear fluid, but of 

 the nature and use of this fluid I cannot speak. In 

 the coloration there is a sharp division between the 



