84 MR. H. CHARLTON BASTIAN S MONOGRAPH 



(liiice, \d{\\ Avliom they arc frequently associated, and also from the Annelids generally. 

 Otiier luovenients of the aquatic species may be well seen if these animals are placed in a 

 watch-glass and examined by a low power of the microscope, when they may be observed 

 twining amongst the branches of the aquatic plants or algie which they frequent, their 

 gliding movements suggesting a resemblance to tiny serpents, till the delusion is banished 

 by a sudden change in their method of proceeding, Avlien, anchoring themselves firmly 

 bv means of their caudal sucker, they continue for some minutes swaying about with the 

 gi'eatest rapidity, darting their bodies hither and thither, and bending in all directions. 



With respect to food, the free Nematodes seem to be almost exclusively vegetable 

 feeders, though it is not often easy to recognize anything definite within their ali- 

 mentary canal — the usual contents being a kind of granular debris, and in several 

 species large oil-globules. In individuals of the genera Cyatholaiiniis and SpUophora, 

 however, I have frequently seen the intestine filled with large DiatomaccDS, whilst in 

 species of other genera I have occasionally made out a few cells of algoe. The quantity 

 of large fat-globules often seen within the intestinal canal is remarkable, and also 

 interesting in a physiological point of view, as an exemplification of the almost direct 

 conversion of cellulose into fat and other products. In Dorylaimus staynalis these large 

 beads of fat are generally of a bright yellow, whilst in other species I have occasionally 

 found them of a pure emerald-green colour, and in one instance even of a distinct magenta 

 hue; bu-t in the majority of species the fat is colourless. I have never yet seen one 

 of these animals swallow a particle of food ; but what they do take appears to remain 

 a long time within the intestinal canal, becoming slowly and almost entirely metamor- 

 phosed into fat, as the primary stage of assimilation. In this respect they differ notably 

 from the NauUnce, Avith which they are usually associated in both fresh- and salt-water 

 mud ; for with these, as with their near ally the Eartlnvorm, the intestinal canal may be 

 considered as little else than a highway road along which extraneous matter, containing 

 organic particles, is continually passing. These latter animals are less fastidious in their 

 appetites, swallowing at random, and appropriating the organic material only when 

 within the alimentary tube ; whilst the Nematodes are selective from the first, taking 

 nothing but such vegetable substances as constitute their particular food. Their powers 

 of prehension seem very limited ; and I believe, from what I have seen, that their food is 

 taken partly by suction, this being effected by the sudden dilatation of the otherwise 

 habitually closed triquetrous canal of the cesophagus, by means of the radiating transverse 

 muscular fibres of which its walls are composed. This rapid dilatation causes an inrush 

 of fluid, with any particles that may be in front of the mouth ; and I have several times 

 observed air-bubbles and fluid enter and pass along the oesophagus in this way. How or 

 of what nature is the food taken by individuals of the genera Bonjlaimus, Tylelcnchns, 

 and Cephalobns, having a sharp, exsertile, spear-like commencement of the oesophagus, I 

 cannot say : it seems difficult to account for the presence of such a structure, unless it 

 were destined to pierce animal or vegetable tissues, and thus enable them to suck the 

 organic juices — a supposition which seems borne out also by the thread-like dimensions 

 of the oesophageal canal in the genus Tyleleiichus. The so-called gastric teeth met with 

 in some of the free as well as the parasitic Nematodes, in the terminal dilated portion of 



