678 THE ANIMAL KINGDOM. 



spends to each lateral area, two are submedian and dorsal, two submedian 

 and ventral ; of the posterior, one corresponds to each of the two median 

 lines, the dorsal and ventral, whilst two on each side are sublateral, i. e. 

 submedian, and are imbedded in the subcuticula. The dorsal median 

 nerve extends to the tip of the tail ; the ventral divides just in front of the 

 anus, and its two branches pass to the sides of the rectum, in the female 

 backwards to the lateral areae, supplying the two sensory papillae, whereas 

 in the male the chief part of the fibres turn forwards in the lateral areae, 

 and supply the bursal muscles. Subcutaneous, transverse, and paired fibres 

 connect the dorsal and ventral median nerves, especially in the head and 

 tail. The median and ventral nerve arises by two short roots ; but in Plectus 

 (sp. ?) there are two ventral nerves fused only posteriorly, and connected 

 from place to place by transverse commissures. Two similar ventral nerves 

 have been also met with in the young Ascaris (Joseph). Ganglion cells 

 are found in the oesophageal ring, chiefly at the origins of the nerves ; in 

 the circumoral plexus into which the anterior nerves pass, in the anterior 

 lateral nerves, in the ventral median nerve, and in the bursal nerves of the 

 male. In the larger Ascarides at least (A. megalocephala, A. lumbricoides\ 

 there is a well-marked ganglion at the spot where the ventral nerve bifur- 

 cates, and in the male a circumanal ganglionic ring (Rohde). Organs of 

 special sense are represented by sensory cutaneous papillae, and by eyes. 

 The former are widely distributed, and occur as oral papillae placed on 

 the lips, or on the cuticle round the mouth, on the neck, at the sides of the 

 anus, and on the ventral aspect of the tail in the male. These papillae 

 project in part, and are in part imbedded in the cuticle. A single nerve- 

 fibre has been traced into a papilla, and the granular mass which occupies 

 its centre is probably a sensory nerve-bulb. Eyes are confined entirely 

 to the free-living genera, and are situated anteriorly in the region of the 

 nerve-ring. They consist, so far as is known, of a mass of pigment, black, 

 brown, or blue, which may or may not inclose lens-like bodies. 



There is a coelome, which in most cases does not form a large cavity ; 

 but whatever space there may be, it is largest round the oesophagus and in 

 the tail. It is traversed by fibres which may be muscular in nature, and 

 appear to be in connection with the fibres of the subcuticula. The coelomic 

 fluid is clear and coagulable, but it is doubtful whether or no it contains 

 any corpuscles. It is often reddish in colour, but this occurs only when 

 the worm feeds on blood, e. g. Syngamus trachealis. The red colour is due 

 to discharged oxy-haemoglobin, and gradually disappears if the animal is 

 isolated and starved. 



The digestive tract appears to undergo regressive changes in Sphae- 

 rularia, and its several parts are said not to communicate in Mermis. The 

 mouth is either anterior and terminal, or else it opens, as in Strongylus, 

 Dockmius, Sclerostomum, &c., into a more or less spheroidal cavity, which 



