ICHNEUMON-FLIES 555 



three clays of work, it dies. In the case of Thalessa it is stated 

 that it sometimes bores into wood where there are no larvae, but 

 Riley thinks this erroneous ; it is, on the other hand, certain 

 that the Insect after penetrating the wood is frequently unable 

 to withdraw the ovipositor, and consequently dies. 



Packard has recorded, 1 without mentioning the species, the 

 oviposition of an Ichneumon of which the egg is deposited 

 externally. It was placed on the head of the caterpillar, and 

 speedily hatched ; the young larva at once bored through the 

 prothoracic segment of the victim, the head of the latter then 

 became swollen, and covered the opening into the prothorax, made 

 by the parasite. 



The history of an Ichneumon larva that feeds as an external 

 parasite has been sketched by De Geer and Newport. The 

 observations of the latter 2 refer to Paniscus virgatus ; he 

 found small, shining, black bodies attached to the skin of the 

 larva of a moth, Mamestra pisi ; these were the eggs of the 

 Ichneumon. They are furnished with a short peduncle, which 

 is implanted in the skin of the victim ; the egg, according to De 

 Geer, being retained more firmly by the peduncle subsequently 

 swelling, so as to form two knobs. The hatching takes 

 place by the egg-shell splitting longitudinally, while from the 

 split protrudes the little head of the destroying larva. This 

 becomes fixed to the caterpillar, from which the nutriment is 

 to be drawn ; the Paniscus larva does not, however, leave the 

 egg-shell, but, on the contrary, 

 becomes adherent to it, so that 

 the parasite is in this manner 

 fixed by the two ends to its 

 victim. In fifteen days the 



parasite was full-grown, and had , 



* . . FIG. 363. Young larva of Pamscus in 



become half ail inch in length. position of feeding on the skin of Mam- 



At first no tracheae were <f - ( After New P rt -) . The e sg- 



shell. 



to be seen, but these were 



detected after the second day. Moulting took place three 

 times, and in a peculiar manner, very different from that 

 described by Eatzeburg as occurring in the internal parasites 

 (which, he states, change their very delicate skin by detaching it 

 in almost imperceptible fragments). In the external parasite the 

 1 Fifth Rep. U. S. Ent. Comm. 1890, p. 15. 2 Tr. Linn. Soc. xxi. 1852, p. 71. 



