224 INSECT TRANSFORMATION 



conspicuous are the Ichneumonoidea slender, wasp-like insects 

 of which there are several families (Ichneumonidae, Braconidae, 

 etc.). All have formidable ovipositors, by means of which 

 they pierce the cuticle and skin of the host, and thus place 

 their eggs inside the body. Some, such as Rhyssa with ovi- 

 positors of enormous length can bore through the bark and 

 wood of trees and thus reach the tunnels of the timber-eating 

 larvae in which their grubs feed. Large ichneumons, like 

 phi on and Pimpla, lay one egg in each caterpillar they 

 attack ; the ichneumon larva may eat its way out of the host 

 before the latter has become full-fed, and spin on the food-plant 

 or on the ground the cocoon in which its pupal stage is passed ; 

 or it may not emerge from the host-caterpillar until this has 

 spun its own cocoon, the last act it is able to perform before 

 dying, a victim to its parasite which then, emerging from the 

 shrivelled cuticle, spins its own cocoon inside the host's, so 

 that the emerging ichneumon-fly has two cocoon walls to pierce 

 before emergence. Small ichneumonoids such as species 

 of the Braconid genus Apanteles lay many eggs in one good- 

 sized caterpillar, the dried cuticle of which may be seen pierced 

 by the holes through which the little parasitic grubs emerge 

 (Fig. 112 a) and surrounded by the silken cocoons, in which they 

 pupate after emergence (Fig. 112 b). All these ichneumonoid 

 grubs are legless and with small heads, like those of bees and 

 wasps (p. 126), and the great majority of hymenopterous larvae. 

 Some of these hymenopterous parasites are noteworthy as 

 affording examples of different forms succeeding each other 

 in the same life-history (hypermetamorphosis, p. 116). Species 

 of Platygaster lay their eggs in some of the larvae of midges 

 mentioned above as living in galls on willow (p. 211). The 

 newly-hatched larva of Platygaster 1 (Fig. 113 A) is remarkably 

 like a little copepod crustacean, having a large, oval front-region 

 comprising the head and thorax, with short feelers and biting 

 mandibles, and a narrow abdomen with a reduced number 

 of segments. This is succeeded by a second stage (Fig. 113 B), 

 in which the body is elliptical in outline, not differentiated into 

 regions, and with the segmentation generally undefined. Not 

 until its third stage does the Platygaster larva assume the form 



1 J. Ganin : " Beitrage zur Kenntniss der Entwiklungsgeschichte bei 

 den Insekten ". Zeisch. f. wissensch. Zoolog., XIX. 1869. 



