226 



THE INVERTEBRATA 



as the well-known plant parasites) the adult female and innumerable 

 larvae are found in the body cavity of the bark beetle, Ips^ during the 

 winter. Allantonema has similar relations to another bark beetle, 

 Hylobius. The female is enormously developed, the uterus and other 

 female organs occupy the whole of the body, the gut having entirely 

 disappeared. In the spring the larvae (having undergone two moults) 

 bore through the walls of the end gut and undergo further develop- 

 ment in the "frass" (faeces of the beetle). The male develops pre- 

 cociously and fertilizes the female which, when it becomes mature, 

 is still of normal proportions. After fertilization the females (only) 



Fig. 171. Insect and plant parasites. A, Atractonema. Female showing the 

 beginning of the prolapsus of the uterus, which has proceeded in Spherularia, 

 B and C, until it is far larger than the rest of the worm. In C, the body is a 

 minute appendage (bd.) of the prolapsed uterus (ut.pr.) not much longer than 

 one of the greatly enlarged cells of the latter. D, Heterodera; 1 and 2, larvae 

 attached to a rootlet with their heads imbedded in its tissues ; 3, the full-grown 

 female (on a smaller scale), removed from the plant. The alimentary canal is 

 shown in black to emphasize that its growth causes the increase in size of the 

 parasite, o. ovary; ut. uterus. A-C, after Leuckart; D, after Strubell. 



infect the beetle larvae which by this time have appeared. Entrance 

 is obtained by means of a *'dart" exactly like the similar organ in 

 the plant parasites. In the body cavity the female Allantonema grows 

 rapidly, and when metamorphosis occurs and the mature bark beetle 

 seeks another tree to form a new colony, it is full of larvae. 



Spherularia (Fig. 171 B, C) is a parasite of the humble bee. In the 

 summer the moss and soil near the bee's nest is inhabited by the 

 sexually mature worms, and after fertilization has taken place the 

 female wanders into the body cavity of the insect, as in the preceding 

 life histories. Though the number of cells in the somatic tissues of the 



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