382 THE SENSORIAL FUNCTIONS. 



assignment of their proper station in the scale of 

 animals. 



Although the power of receiving obscure im- 

 pressions from the contact of external bodies, 

 and of perceiving variations of temperature, is 

 probably possessed by all animals, a small num- 

 ber only are provided with organs specially 

 appropriated for conveying the more delicate 

 sensations of touch. The greater part of the 

 surface of the body in the testaceous Mollusca is 

 protected by a hard and insensible covering of 

 shell. The integuments of Insects, especially 

 those of the Coleoptera, are in general too rigid 

 to receive any fine impressions from the bodies 

 which may come in contact with them ; and the 

 same observation applies, with even greater force, 

 to the Crustacea. The scales of Fishes, and of 

 Reptiles, the solid encasements of the Chelonia, 

 the plumage of Birds, the dense coating of the 

 Armadillo, the thick hides of the Rhinoceros, 

 and other Pachydermata, are evidently incom- 

 patible with any delicacy of touch. This nicer 

 faculty of discrimination can be enjoyed only 

 by animals having a soft and flexible integu- 

 ment, such as all the naked Zoophytes, Worms, 

 and Mollusca, among the lower orders, and Ser- 

 pents, among the higher. The flexibility of the 

 body or limbs is another condition which is ex- 

 tremely necessary towards procuring extensive 

 and correct notions of the relative positions of 

 external objects. It is essential therefore that 



