v ASCARIS 181 



consists of a simple layer of tall epithelial cells, bounded both externally 

 and internally by a distinct cuticle-like membrane. 



There is no layer of coelomic epithelium covmnu r the surface of the 

 alimentary canal and it is indeed quite uncertain whether the body- 

 cavity through which the alimentary canal runs is really a true coelome 

 at all. 



Towards the anterior end of the worm the body-cavity contains four 

 remarkable structures known as the phagocytic organs, which can be 

 distinctly seen as dark shadows if the fresh worm is held close to a strong 

 light. In a dissection they are seen as small fluffy objects, of a pinkish 

 or brownish colour, lying between the alimentary canal and the body-wall. 

 Although arranged in two pairs the members of each pair are not exactly 

 opposite one another but are arranged obliquely. Microscopic examina- 

 tion shows that each organ consists of an enormous cell, the body of which 

 extends into tree-like branches which serve to anchor it to the body-wall 

 and the intestinal wall. Both cytoplasm and nucleus of the cell are con- 

 verted into a stiff material so that the cell and its branches are fairly 

 rigid. This cell serves a mainly supporting function, its branches 

 acting as supports to numerous little blobs of protoplasm which are 

 perched all over them. These protoplasmic blobs are actively phagocytic, 

 i.e. they serve to ingest solid particles of a harmful nature which may 

 come to be in the fluid of the body-cavity. 



The reproductive organs of Ascaris are of a characteristic type. In 

 the female the external genital opening (Fig. 81, $ ) is a small pore, situated 

 mid-ventrally in a slightly marked shallow groove which encircles the 

 body at a very variable position in the anterior half or third of its length. 

 This opening leads into a vagina and this at its inner end bifurcates 

 to form the two uteri. Each uterus is a thick tube of considerable length, 

 normally packed with eggs (Fig. 82, ut). The eggs are enclosed in thick 

 shells of distinctive appearance (Fig. 90, B) and of extraordinary 

 impermeability so that they may remain alive for many months after 

 the adult is placed in a strong preserving fluid such as formalin. 

 The uterus is continued into the oviduct (Fig. 82, od} a much narrower 

 tube which normally contains scattered eggs without any shell the eggs 

 not yet having been fertilized and this in turn is continued into the 

 actual gonad. The gonad of the nematode is of very characteristic 

 appearance, consisting of a greatly elongated thread which tapers off 

 at its end into an extremely fine, freely ending, filament. In trans- 

 verse section (Fig. 82, ov) the gonad shows an equally character- 

 istic arrangement of genital cells radiating out from a solid core 

 of protoplasm known as the rachis. As the gonad merges into the 



