NEMATODA. 677 



been supposed to be muscular in nature, and continuous, in part at least, 

 with the extremities of the muscle-cells. These fibres are especially well 

 developed in the rectum. The subcuticula is thickened internally, as a rule 

 in four longitudinal lines, a median dorsal, a median ventral, and two 

 lateral, one on either side. The latter are especially prominent, and are 

 generally known as the ( lateral areae. 5 The dorsal and ventral lines are 

 probably always present, the lateral except in Trichocephalus , and perhaps 

 some others. Cutaneous glands are absent 1 . The muscles of the body- 

 wall consist of a single layer of longitudinally disposed muscle-cells. In 

 these cells the contractile substance is fibrillate, and forms a superficial 

 stratum on the basal part of the cell, which is applied to the subcuticula in 

 the Meromyarii of Schneider (e. g. Oxyuris, Strongyhts), or on the base, the 

 sides, and ends of the cells, as in other Nematoda. The body of the 

 muscle-cells consists of a feebly granular protoplasm or medulla in which 

 a nucleus may be found. This medulla projects freely on the inner or 

 coelomic aspect of the cell to a variable degree, and over a variable extent 

 of that aspect. The projection is greatest in the Coelomyarii of Schneider 

 (e. g. Ascaris, Filaria], in which protoplasmic bands connect it to the 

 median ventral or dorsal lines, to the lateral areae, or to both. The ends 

 of the muscle-cells are said to break up into processes, which are traceable 

 into the fibres of the subcuticula. The number of cells visible in a trans- 

 verse section is usually very great, but in the Meromyarian Nematoda 

 there are only eight, two lying in each of the four quadrants limited by the 

 median lines and lateral areae 2 . In addition to the body-muscles there 

 are certain others ; the exsertors and protractors of the male spicules ; a 

 paired ventral muscle which is the cause of the curvature in the tail. The 

 radial muscles which are connected to the mesenteron and are of all, those 

 most obviously prolonged into the fibres of the subcuticula ; the dorso- 

 ventral and latero-ventral muscles which cross the body behind the anus ; 

 the bursal muscles which pass in a similar direction, and are present only 

 in the male ; have a different structure. They are nucleated, but their 

 medulla and contractile fibrillae are intermixed. 



The nervous system, said to be absent in some of the free-living 

 genera, consists of a fibrous ring surrounding the oesophagus, at a little 

 distance from the anterior extremity. Six nerves originate from this 

 ring both anteriorly and posteriorly. Of the anterior nerves one corre- 



1 Long pear-shaped glands, open by a common duct on the ventral aspect, and near the tip of 

 the tail in the free-living marine genus Enoplus. They secrete a tenacious substance, by which 

 the animal anchors itself. They are perhaps present in some fresh-water forms. 



2 Schneider supposed that in certain Nematoda, e. g. Trichina, Trichocephalus, the muscles of 

 the body- wall were ' either not divided, or only divided in a longitudinal direction,' i. e. by the lateral 

 areae and median lines. Such Nematoda he classed as Holomyarii. There are, however, numerous 

 muscle-cells in all so-called Holomyarian genera which have been carefully re-examined, e. g. in 

 those named above and in Mermis. See Biltschli, ' Giebt es Holomyariif Z. W. Z. xxiii. 1873. 



