fresh water biolgoy

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1918 Excerpt: ... the remainder of the surface has the typical nematode appearance. The body tapers slightly towards one or both ends and only very rarely can one find marked differences in diameter or dis Some authors designate the class Nematomorpha and rank the Gordiacea as an order under it. tinguish adjacent regions by other prominent features. As a rule the anterior end is slightly blunter whereas the posterior end is more pointed. The uniformity of external appearance is very characteristic of nematodes. This creates an impression of monotony in structure and renders their classification difficult The smaller forms are somewhat transparent in life but the larger species are opaque. One may also recognize a nematode easily by its peculiar type of movement, which in a liquid medium consists of a more or less rapid and violent coiling and twisting alternately right and left without appreciable progress, but is modified by the presence of solid particles in the fluid into a powerful serpentine movement winding in and out among the debris. This grows in effectiveness as the material becomes more nearly solid and the particles are less readily pushed aside by the twisting of the worm. In external features the parasitic species appear somewhat different from the free-living forms. On the whole they are much larger, thicker and more opaque. Few species are as minute as free forms and only these minute types approach the free species in transparency. The external form is also more monotonous since the delicate hairs and scales that distinguish free species are almost entirely wanting. Eyes, amphids, and setose tactile organs such as already described for free-living types are not present in parasitic species. Parasitic nematodes occur in nearly all water-living vertebrates; t...