236 ANIMAL PHYSIOLOGY. [LESSON 71. 



no power to direct or organize motion ; neither is a motor nerve en- 

 dowed with sensation. 



A nerve of vision cannot perform the function of smell, taste, 

 hearing, or touch ; neither can the nerves of one organ assume the 

 function of the nerves delegated to another organ; each has its own 

 duty to perform, preserves its individuality, and is so far distinct. 



1070. A nerve and a ganglion, as will be hereafter seen, possess, 

 each of them, a peculiar and definite structure, and the only way to 

 be sure of their presence is to cut off a small portion, and examine 

 it with the high power of a compound achromatic microscope. 



1071. Plants assimilate food, continue their kind, and the lower 

 orders of them are even endowed with locomotion ; the Venus' Fly- 

 trap, and the Sensitive Plant would seem to offer the indications 

 of a nervous system ; so far as is really known, the lower animals 

 appear to occupy a similar position with plants. 



1072. From the foregoing statement, it will be advisable to com- 

 mence the inquiry into the nature and condition of the nervous sys- 

 tem, and its mode of development, in the Articulate sub-kingdom, all 

 the individuals included in this section being unmistakably endowed 

 therewith. 



LESSON LXXI. 



NEBYOTJS SYSTEM IN THE AETICULATA. ENTOZOA ANNELLIDA. 



1073. In the lowest animals of this sub-kingdom, the parasitic 

 Entozoa, the nervous system is very imperfectly developed, and, from 

 their position within the bodies of other animals, but little required. 



1074. In the intestinal parasite Strongylus gigas, a slender ner- 

 vous ring surrounds the beginning of the gullet, and a single chord 

 is continued from its inferior part, and extends in a straight line 

 along the middle of the ventral aspect to the opposite extremity of 

 the body, where a slight swelling (ganglion) is formed, immediately 

 anterior to the posterior part of the body, which is surrounded by a 

 loop, analogous to that with which the nervous chord commenced. 

 The abdominal nerve is situated internal to the longitudinal muscular 

 fibres, and is easily distinguishable from them with the naked eye, by 

 its whiter color, and the slender branches which it sends off on each 

 side. These transverse twigs are given off at pretty regular inter- 

 vals of about half a line, and may be traced round to nearly the op- 

 posite side of the body. 



