ORGANS OF SENSE. 65 



especially the lion, and others of the cat kind, it is beset with strong 

 sharp prickles, for prehensile purposes. 



Touch. — This is the most general as well as the most simple of 

 the senses, and the degree in which it exists has reference to the 

 state of the tegnmentary membrane, and I he condition of the nervous 

 system. In the invertebrata no organs solely devoted to the per- 

 ception of sensitive impressions have been detected, yet there is little 

 doubt but that the cilia of most poly wastries, the ten taenia of zoo- 

 phytes and mollusca, and the antennas of ray ri a pods and insects are 

 subservient to this sense. Some fishes have fleshy sensitive fila- 

 ments arranged around the month after the manner of ten taenia, 

 and others have only the skin on the abdomen, or about the mouth, 

 uncovered with scales, and capable of receiving- external impres- 

 sions. The tongue among serpents, and the tail among saurian 

 reptiles, and some mammalia, constitute their chief tactile organs. 

 The organs of touch in birds are the bills, the cire in the falconidce 

 the wattles of the cock, and the caruncles of the turkey. It must 

 be acknowledged, however, that this sense is very limited in birds, 

 which is in some degree compensated for by the free distribution of 

 the fifth pair of nerves to their horny bills, especially those of the 

 aquatic species, which procure their aliment from mud. 



In many of the mammalia the skin is shielded from external im- 

 pressions by the presence of horny or spiny coverings, dense furs. 

 or thick hides; and it is not till we arrive at the higher orders of 

 quadrupeds, carnivora and quadrumana, that the organ of touch 

 makes any approach to the perfect development of it observed in 

 the human subject. 



RECAPITULATION. 



1. Organs of vision exist in every class of animals, and in the 

 lowest orders the eyes vary in number from one to near 100. 



2. In the vertebrata the eyes are two and vary much in form and 

 situation. 



3. No organs of hearing or smell have been detected in the 

 radiata. 



4. Our knowledge concerning the organ of taste is involved in 

 much obscurity. 



5. No organ of touch has been detected in the invertebrata. 



CHAPTER. X 



ORGANS OF DIGESTION IN THE INVERTEBRATA. 



General observations. — The organs engaged in the function of 

 digestion may be arranged under two heads: the primary, or 

 8 — f evers 5 



