264 THE ANIMAL PARASITES OF MAN 



The BODY CAVITY, which lies between the body and intestinal 

 walls, is according to its development not a coelom but the cleavage 

 cavity. It is considerably restricted by the protoplasmatic por- 

 tions of the muscular fibres and by the genitalia ; it contains a 

 small quantity of haemolymph, and sometimes also leucocytes. 



We may now consider the " tuft-like " or " phagocytic organs," 

 which attain i cm. in size, and consist of four, six, or even 

 more ramified cells, which lie close to the walls of the body 

 (fig. 183). They are found either only in the anterior part of 

 the body (Ascaris), or extend the whole length of the body 

 (Sclerostomum, Strongylus), and their position usually corresponds 

 to the lateral ridges. In some species there are small proto- 

 plasmatic cells at their processes. In consequence of their size 

 they can be recognised with the naked eye, especially when loaded 

 with granules of stain (carmine, Indian ink) injected into the 

 body cavity. 1 



INTESTINAL CANAL. The oral aperture, which is situated at the 

 tip of the anterior extremity, is frequently surrounded by thick 

 lips, or small bristles, or papilla? ; it leads to a more or less 

 strongly-developed oral cavity, which is lined by a continuation 

 of the body cuticle, and which in some species is provided with 

 " teeth," representing differentiated portions of the cuticle. 



THE (ESOPHAGUS (fig. 184), which arises from the base of the 

 oral cavity, is as a rule a short, bottle-shaped tube, its wall is 

 chiefly composed of radiating muscular fibres, which give it the 

 appearance of being transversely striped. The radiary fibres cause 

 a dilatation of the lumen, and exercise an effect antagonistic to 

 the elasticity of the cuticle lining the inner surface. The latter 

 has its own particular layer, which is not in direct connection 

 with that of the oral cavity. The posterior end of the oesophagus 

 presents a bulb-like dilatation, and is frequently provided with 

 small teeth. In a few forms, which belong to the family of the 

 Trichotrachlidse (Trichocephalus, Trichinella), the oesophagus is a 

 very long cuticular tube, beset on its dorsal surface with a series 

 of large nucleated cells. In others (Cucullanus, a few species of 

 Ascaris, &c.), a tube, the so-called glandular stomach, only lined 

 by epithelial cells, follows behind the muscular oesophagus. This 

 glandular stomach is, from its structure, easily distinguished from 



1 Nassonow, N., " Sur les org. phagocyt. d. A scar." (Arch, parasit., 1898, i., p. 170). 

 " Z. Kennt. d. phagocyt. Org. b. d. parasit. Nemat." (Arch. f. mikr. An., 1900, lv., p. 

 488). Jagerskiold, L. A., " Ueb. d. bilschelf. Org. b. d. Ascaris-arten " (C. f. B., P. 

 u. I., 1898 [i], xxiv., pp. 737 and 785). 



