IV VERMES— BODY CAVITY 211 



VI. The Body Cavity, the Musculature which passes transversely 

 through it, the Dissepiments and Mesenteries. 



In the Nemertina we cannot yet speak of a body cavity (coelome). 

 Apart from the connective tissue, which penetrates between the 

 muscles of the dermo-muscular tube, the space between the intestine 

 and that tube is everywhere filled by a gelatinous tissue which is 

 morphologically equivalent to the gelatinous tissue of the Gcelenierata 

 and the parenchyma of the Platocles. The various organs — genital 

 glands, blood-vessels, nephridia — are imbedded in this gelatinous tissue. 

 Dorso-ventral muscle fibres pass through it and form (1) a sort of 

 enteric musculature, the intestine passing between them and holding 

 them apart, and (2) passing between the enteric diverticula a sort of 

 muscular septa separating them ; these septa, just like the diverticula 

 themselves, lie one behind the other with more or less regularity, 

 and recall the septa which are developed between the gastro-canals of 

 the Platodes. 



In the Nemathelmia there is a very spacious body cavity filled 

 with fluid, which, in the Nematoda, occupies the whole space between 

 the dermo-muscular tube and the intestine ; and in the Acanthocepluda, 

 where an intestine is wanting, it is represented by the whole interior 

 of the body, which is surrounded by the dermo-muscular tube. In 

 this cavity lie the genital organs, bathed on all sides by the body fluid, 

 and further, in the Acanthocephala, the lemnisci. In the latter the 

 genital organs are attached by a muscular band or ligament to the 

 posterior end of the proboscis sheath, and also by lateral muscular 

 bands to the dermo-muscular tube. The body cavity of the Nematliel- 

 miu is not lined with a special epithelium (endothelium), but is 

 limited directly — externally by the body musculature, and internally by 

 the walls of the intestine. 



The Gordiidce occupy an isolated position among the Kemat- 

 helmiuths in the morphological condition of the ccelome, as in many 

 other points of their organisation. In animals not quite sexually 

 mature we find between the intestine and the body wall a consider- 

 able mass of cells, which disappears for the most part at the time of 

 the development of the genital glands, and is probably used as material 

 for nourishing these glands. We then find, in place of the cell mass, 

 a spacious body cavity, which, however, in contradistinction to other 

 Nemathelminths, is lined on all sides by an epithelium, often of several 

 layers, lying on the inside of the dermo-muscular tube (Fig. 170, p. 

 256). This epithelium, in contrast to the epithelium of the intestinal 

 canal and to the outer body epithelium, we call the peritoneal endo- 

 thelium. This endothelium forms, in the median plane of the body, 

 a partition wall which separates into 2 lamellte ; these run dorso- 

 ventrally, having the intestine between them. At the sides of the 

 ventral median nerve they unite with the endothelium of the body 



