1/2 NEMATHELMINTHES 



as the adult some eighteen or twenty months after it has been 



hatched from the egg. 



From the above account of the life-history of Gordius it will 



be seen that the chances of an egg reaching maturity are com- 

 paratively small, and to compensate 

 for this a very large number of eggs 

 are laid. In addition to the risk of 

 the larvae not finding the right host 

 at the right time, and of the first host 

 not being eaten by the second, and 

 the second not being drowned, there 

 is the danger that the ditches and 

 ponds in which the adults live may 

 dry up, and, in fact, great numbers 



FIG. 90. Embryo or first larval n j 



form of Gordius toiosanus taken of worms perish by this taking place. 



from the egg Highly magni- Th f th d lfc } told 



fied. a ami b, The bristle-bear- 



ing papillae on the head ; c, from their colour, the males being of a 

 ^ 1 ^' (Fr " 1 blackish brown, the females of a light 



clay brown; the former average 120 

 mm. in length, the latter 170 mm. The males are also more 

 numerous, the proportion being seven to three. Camerano 1 has 

 drawn attention to the fact that there is a certain polymorphism 

 in size, form, and colour which is especially common amongst the 

 males ; dwarf forms with mature reproductive organs exist, and 

 he is of opinion that these differences depend both on the size of 

 the second host and on the duration of the parasitic life. 



In addition to the larva of Sialis lutaria, the first larval stage 

 has also been found in the larva of Ephemera, T any pus, Corethra, 

 and Chironomus ; the second in Car alms hortensis Fabr., Procerus 

 (Carabus) coriaceus Linn., Calathus fuscipes Goeze., Molops elatits 

 Fabr., several species of Pterostichus, and a number of other 

 beetles. It is probable that its normal hosts are S. lutaria and 

 PL nigcr, but it is clear that it often comes to rest in other 

 insects. The view that the Gordiidae have no special hosts, but 

 may either pass the whole of their life-history within one and 

 the same animal, or, on the other hand, may inhabit animals 

 belonging to very different groups, is held by Villot, who has 

 paid great attention to the subject. He finds the first larval 

 form encysted in the walls of the alimentary canal in fishes, such 

 1 Zool. An:, vol. x. 1887, p. 602. 



