NOTES OX THE FREE-LIVING NEMATODES. 443 



Biology in Relation to Methods of Experiment. 



To (obtain soil-iiematodes in large quantities,, it is only 

 necessai-y to place scraps of flesh on samples of rich soil or 

 mould kept moist and warm, and wait till decay has set in. 

 Thoug'h the normal nutriment of these animals is presumably 

 associated with the deca,v of vearetable products rather than 

 decomposing- animal matter, the latter prove exceptionally 

 attractive. When once putridity commences, five or six days 

 more suffice for the appearance of very large numbers of 

 rhabdites or diplogasters, generally belonging to one or two 

 species. Before, however, the last remains have vanished, 

 it is probable that other species will have appeared and 

 become dominant, entirely replacing the iirst kinds, so that 

 an alternation is obtained somewhat similar to the succession 

 of Protozoa in putrefying broth. It seems that the soil 

 contains scattered throughout it numerous encysted larvse, 

 for, as Maupas has pointed out, when insufficient nutriment 

 is supplied to soil-nematodes, the young larvas envelop 

 themselves in a thick cuticle, and become rigid and immobile. 

 Tliey are capable, however, of violent contortions, as if for 

 the purpose of freeing themselves from the cyst, and by 

 these movements migrate easily through the soil. The 

 cuticular protection enables them to live uninjured in a dry 

 environment, so that soilj etc., which has been subjected for 

 long periods to fairly high temperatuies, will yet yield large 

 numbers of nematodes when treated in the way described 

 above. The ])ower of encystment, and consequently of 

 resisting prolonged desiccation, is confined to the larvas. 

 Adult worms ao once die when a liquid culture in which 

 they are contained is allowed to dry np, and the eggs of 

 these forms are provided only with a thin cuticular envelope, 

 and are incapable of resisting the vicissitudes to which the 

 eggs of parasitic forms like Ascaris are successfully exposed. 

 When, then, anima.l-niatter putrefies on a sample of soil, it is 

 the encysted larvae which are attracted to its neighbourhood, 

 where tlun- enieri>-e from theii- cvsts and commence to feed 



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