358 NATUEAL HISTOEY. , 



senses and in that of voluntary motion, and also in the 

 nervous system, by which these two kinds of apparatus 

 are connected with the mind.* In the lower orders of 

 animals the senses are very imperfectly developed, and 

 in some most of the senses are absent. Thus, hi the Hy- 

 dra ( 599) and in the Actiniae ( 576) there is no evi- 

 dence of the existence of but one sense, that of touch. 

 The Actiniae are, indeed, sensibly affected by light, but 

 this does not prove that they see. As we go upward in 

 the scale we find the apparatus of the senses generally 

 more and more developed. Taking all of them into view, 

 the senses are best developed in man, though some of 

 them, for special purposes, have a higher capacity in cer- 

 tain animals than in him. Some may have a more acute 

 smell, as the dog-, or see farther, as the eagle ; but no an- 

 imal has all the senses in such perfection as man. The 

 same can be said of the muscular apparatus. The vari- 

 ety of muscular action is greatest of all in man, while in 

 some animals there are special muscular endowments for 

 special purposes above any thing of the kind to be found 

 in him. The gradation in the nervous system is still 

 more definitely marked. In man it has its fullest devel- 

 opment ; 'and, as we go down in the scale, we at length 

 come to animals that have no distinct brain, and finally 

 to those in which, as the hydra, no trace of any thing 

 like a nerve can be found. In these last nervous matter 

 is presumed to exist because actions are performed which, 

 in animals of a more defined organization, are known to 

 be dependent upon nervous agency. 



624. Amid all the variations of structure to suit the 

 different wants and capabilities of animals, the Creator 

 has adopted certain general plans, so that order prevails 

 throughout all the extreme variety of the animal king- 

 dom. "We can see this whether we take into view large 



* For the relations of the senses, the muscles, and the nervous sys- 

 tem, I refer you to the chapter on the Nervous System in my "First 

 Book in Physiology." 



