NEMATODA AND NEMATOMORPHA 257 



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) 

 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. 178 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 

 bee is said not to increase in number there is an enormous growth in 

 size of the vagina which becomes prolapsed and forms eventually an 

 organ many times the size of the rest of the body, which remains 

 attached for some time but eventually disappears. The parasitized 

 humble bees, after passing the winter in their nests, tend to emerge 

 early. In the spring very often inactive bees may be caught which 

 prove, on dissection, to contain one or more of these enormous 

 sausage-shaped bodies, each of them full of eggs and larvae, which 

 escape through the gut wall and become free-living. 



Atractonema (Fig. 178 A), a parasite of the Cecidomyidae (p. 509), 

 has a similar life history. 



PHYLUM NEMATOMORPHA 



As in Nematoda but lateral line and "excretory" canal absent, 

 nervous system consisting of a dorsal "brain" and a single ventral 

 cord, genital ducts in both sexes opening into the hind gut to form a 

 cloaca, development very characteristic — gastrulation by invagination 

 and a larva with peculiar boring organ which infects insects. 



In addition it should be mentioned that the alimentary canal is 

 always more or less degenerate and the body cavity may either be 

 occupied by parenchymatous tissue or by reduction of this becomes 

 more or less empty of cells. 



An example of this group is Gordius robustus with the following life 

 history. The adults are found in brooks from October till May when 

 they copulate. The sperm is not directly introduced into the cloaca, 

 but placed in masses on the body near it. The eggs are laid in the 

 water and the larvae soon hatch. By using the boring organ which 

 they possess they find their way into the body cavity of crickets which 



