chap, vi NEMATODA EXCRETORY SYSTEM I 33 



the last named there are many cells in a transverse section. 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 1 in the genus Lecano- 

 eephalus. 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 

 Dock mi us have a similar internal opening; these observations, if 

 confirmed, 2 show a conformity to the ordinary structure of ex- 



1 SB. Ah. Berlin, 1891, p. 57. [ 2 Hamann subsequently withdrew thts<> statements.] 



