Notes on the Free-Living Nematodes

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Abstract
Orley divided the Nematoda into three groups, roughly corresponding to differences of habitat found in the phylum. (1) Nematozoa embracing all parasitic forms, (2) Rhabditiforniæ which live free in “decomposing organic substances or in earth saturated with such substances”; and (3) Angui 1-lulidæ, the rest of.the free-living nematodes, found in soil oiwater. Such a classification, grounded on œcology, pays no attention to the facts of morphology, and is naturally out of place in zoological arrangement, which aims at expressing the relationship of animals by descent. The methods of life of an animal are, moreover, largely ruled by the mode oE procuring nutriment which has been adopted. The first two groups of Orley are parasites and saprophytes respectively, but in the Anguillulidæ we have a heterogeneous collection of forms varying greatly in their habits of life. Little is known of their sources of nourishment save in the case of a very definite division (e.g. Tylenchus, Dorylaimus), which live on the juices of plants, and for that end are provided with a small protrusible spear for piercing tissues and suctorial pharynx for absorbing sap thus set free. The vast majority of this family, however, possess an unarmed buccal cavity; but in all the muscular pharynx is constantly at work, now dilated, now collapsed, constantly pumping fluid through the alimentary canal. There is no morphological distinction to be observed between such a free-living nematode as is found in. the mud of a lake or amongst the algæ of the marine littoral anda Rhabditisor Diplogaster of the soil. But the latter class can be kept in a culture fluid which swarms with bacteria, in which individuals of the former class would speedily succumb. The tissues of a Rhabdi tis must be resistant to bacterial action and unharmed by the toxins which such organisms produce, and the worm is, in fact, capable of building up protoplasm from the bacteria themselves or from the products of their action. These are the most prominent physiological characteristics of the soil nematodes, Orley’s Rhabditiformæ, and account for the peculiarities of their distribution, for they are apparently absent from dry soils and those with a small admixture of organic matter, and even in soils rich in humus are only detected in quantity by allowing some animal or vegetable substance to putrefy on the sample. Sufficient attention has not been paid to the part which nematodes play in the economy of the soil,1 but an investigation of this problem may well reveal results of as great interest as those which have been put on record by Maupas, working on the sexual organisation. In the present paper it is proposed to confine attention to the reproductive phenomena in certain hermaphrodite species, but it is hoped in a subsequent research to return to the nutrition and distribution of the class.

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