ORGANS OF TOUCH AMONG LOWER ANIMALS. 11 



termination of the nerves corresponding to these differ- 

 ent sensations, though it may reasonably be expected 

 that such must exist. 



The question has arisen whether there are separate 

 nerve-endings for pain, as apart from pressure, etc. ; but 

 the observations of Blix and Goldschneider appear to 

 show that pain arises merely from the intensification of 

 other impressions, and that it does not reside in any 

 special organs. 



Sense of Touch among the Lower Animals. 



Among the lower animals the outer skin is often 

 very sensitive, but we know scarcely anything as to the 

 minute structure of the organs of tactile perception. 

 In some cases they are, no doubt, very simple ; but in 

 others it will probably be found that the apparent 

 simplicity is due to our deficient information and means 

 of investigation, rather than to any want of complexity 

 in the organs themselves. 



In the Coelenterata (zoophytes, etc.) certain setse, 

 especially on the tentacles and near the mouth, are 

 generally regarded as organs of touch. 



In the epithelium of many of the lower animals, two 

 forms of cells may be detected. Some unmodified, or 

 indifferent, which form the general substance of the 

 epithelial layer ; others more or less specialized, which 

 are seldom absolutely contiguous, but generally sepa- 

 rated by one or more of the indifferent cells. 



In other cases, nerves may end abruptly at the 

 cuticle without the latter presenting, so far as our 

 present means of investigation have shown, any ap- 

 parent change; as, for instance, in the following 



