CHAP. V.] THE NERVOUS SYSTEM OF VERMES. 87 



which receive fibres from certain large papillae surrounding 

 the mouth. These papillae would seem to be the principal 

 sensory organs of the Nematoid. By means of the connect- 

 ing nerve-fibres and ganglion-cells they are brought into 

 relation with the nervous ring, and from this latter out- 

 going fibres are, doubtless, given off to the four great 

 longitudinal muscular bands by which the movements of 

 the organism are effected. The distribution of such motor 

 nerve-fibres, however, has not been distinctly traced. 



The absence of ganglionic swellings on, or in connec- 

 tion with, the cesophageal ring of Nematoids is probably 

 dependent upon the comparative simplicity and limited 

 number of the impressions capable of being received 

 through their cephalic papillae. 



Among other representatives of the sub - kingdom 

 VERMES, the nervous system varies a good deal in minor 

 details, in accordance with the degree of organization, and 

 with the diversity of the sensory and locomotor endow- 

 ments of the several organisms. The broad features of 

 the nervous system, however, are comparatively similar 

 in all especially in the most typical representatives of 

 this sub-kingdom, which contains so many aberrant types. 

 Only a very few forms will be here referred to. 



The Nemerteans, a class of marine worms, possess 

 a very simple nervous system. They have soft, un- 

 segmented, and highly contractile bodies, covered with 

 cilia, but are otherwise wholly devoid of all external 

 appendages. On the anterior extremity of the body, a little 

 posterior to the mouth, two, four, or more specks of pig- 

 ment are met with (fig. 30, e, e), which are conjectured to 

 serve the purpose of rudimentary ocelli ; and whilst the 

 animal is moving from place to place this anterior part of 

 its body doubtless acts also as its principal tactile surface. 

 Nerve-fibres proceed from these regions, and converge so 



