NEMATODA 



[CH. 



5- 



outermost layer of the muscle-cell is con- 

 verted into fibrils, the great bulk consist- 

 ing of unmodified protoplasm, which is 

 often drawn out into an internal process 

 running towards the dorsal or ventral 

 ectodermal ridge. Muscle-cells of such a 

 character are known only in Nematoda. 



The body-wall, which has just been 

 described, encloses a space which is 

 traversed from end to end by the ali- 

 mentary canal. This space is full of fluid 

 and it lodges the reproductive system. 

 It has no epithelial lining and is a 

 primary body-cavity and the only repre- 

 sentative of blood is the fluid which it 

 contains. 



The mouth is terminal and is usually 

 surrounded by certain papillae or lobes, 

 often three or six in number. It leads 

 (if, s into an oesophagus, usually with a tri- 

 angular cavity and thick muscular walls 

 (Fig. 54). The oesophagus may be 

 immediately followed by a second mus- 

 cular bulb, called the pharynx, which 

 sometimes has an armature of some 

 2 bristles or spines. Both oesophagus 

 and pharynx are parts of the stomo- 

 daeum. Then follows the intestine, 

 which is by far the largest part of the 

 alimentary canal. The muscular oeso- 

 phagus no doubt acts as a sucking organ, 

 but there are no muscles and no cilia 

 in the intestine. It is a simple tube 

 formed of a single layer of cells, which 

 both .inside and out secrete a thin 

 cuticle. Posteriorly it passes into a 



Fio. 54. Female Ascaris lumbricoides, cut open along the median dorsal 

 line to show the internal organs x 1. 



1. The muscular oesophagus. 2. The intestine. 3. The ovary. 4. The 

 uterus. 5. The vagina. 6. Its external opening. ' 7. The 



excretory canals. Q. Their opening. 



