{132}[Illustration: FIG. 65.—A longitudinal section through the body of _Strongylus filaria_ Rud. (From O. Augstein.[165]) A portion of the body, on each side of the excretory pore, is seen in optical section. _a_, Mouth; _b_, oesophagus; _c_, intestine; _d_, excretory canal; _e_, excretory pore, and the opening of the poison glands, _i_; _f_, circumoesophageal nerve-ring; _g_, ventral nerve; _h_, dorsal nerve; _i_, unicellular poison glands; _k_, ovary, with the ova separate; _l_, oviduct; _m_, uterus, the first egg in the uterus is surrounded by spermatozoa; _n_, opening of uterus; _o_, inner end of ovary with the ova undifferentiated.] {133}In some genera, _Leptodera_ and _Pelodera_, the lumen of the intestine at any one level is bounded by two horseshoe-shaped cells, but by far the commonest arrangement is a tube formed of fairly numerous columnar cells crowded with granules and with large nuclei. The rectum is usually short; its cuticular lining, like that of the oesophagus, is cast at intervals. At its anterior end there is usually a sphincter muscle, and its walls are divaricated by muscular strands which run from it to the body-wall. The anus is a transverse slit, which in the male Strongylidae is surrounded by a funnel-shaped membrane. The food of Nematodes seems to be almost entirely fluid, and consists, at any rate in the parasitic forms, of the elaborated juices of their hosts. Little is known about the nutriment of the free-living forms. THE EXCRETORY SYSTEM.—The excretory organs are peculiar, and, like many other Nematode structures, do not fall readily into line with what is known of similar organs in other animals. They consist of two canals embedded in the lateral thickenings of the sub-cuticular tissue. The canals end blindly behind, but near the anterior end of the body they bend inwards, and after uniting, open by a common pore situated in the middle ventral line, a little way behind the mouth. The lateral canals are in some cases continued in front of the transverse branch, and they then end blindly in the head. The walls of these canals consist of an internal, structureless, refractive layer surrounded by a granular layer with nuclei. They contain a fluid, but nothing is known of its composition. An interesting divergence from the usual form of excretory organ has been described by Hamann[166] in the genus _Lecanocephalus_. Here there is only one canal, the right; anteriorly this bends towards the ventral surface and opens by a small median pore close behind the nerve-ring. Posteriorly the canal does not extend much beyond the middle of the body, where it forms a coiled mass, and diminishing in size, opens into the body-cavity. The same author also states that both canals in _Dochmius_ have a similar internal opening; these observations, if confirmed,[167] show a conformity to the ordinary structure of {134}excretory organs which was not supposed to exist in the lateral canals of the Nematoda.