180 



ZOOLOGY. 



n 



cunse.|uently, the more organs there are endowed with 

 peculiar OT specific kinds of activity, diii'erinj,' from each 

 other, the more numerous will be the number of dissimilar 

 part> in tin- animal economy; and the complication more 

 or less great in the acts and faculties of animals must 

 pro. <>cd,pari passu, with the natural complication of their 

 organization. 



347. Thus in those animals in which the faculties are 

 the most limited, and in which life exhibits itself in its 

 simplest form, the body presents everywhere the same 

 structure. There is in fact a seeming identity of organization 

 throughout. Every part of the body performs the same 



functions as the neighbouring 

 parts. If divided into seg- 



ments, each part lives, and 

 becomes an independent ani- 

 mal as complete as that from 

 which it was violently sepa- 

 rated. 



The fresh water polyp or 

 hydra is an animal of this 

 kind. By mutilation it is 

 multiplied instead of being 

 destroyed. We owe the dis- 

 covery of these curious facts 

 to Trembley, a Swiss natu- 

 ralist of the last century. 



The simplicity of the orga- 

 nization of these animals can 

 only be demonstrated by the 

 microscope, under which the 



Fig. 130. Hydra.* substance of their body ap- 



pears throughout identical: 



it is composed of a gelatinous -mass, enclosing fibrils ami 

 globules extremely minute. Now identity of structure would 

 imply identity of function, and the experiments of Trembley 

 proved the correctness of the inference. 



* In figure 120 several polyps are represented as attached to water- 

 li-ntils, a ; they consist of a single gelatinous tube, open at one of its 

 -\i Trinities, and furnished with a circle of filaments called tentacula, by 

 means of which they introduce into their bodies the food they require. One 

 "f tin-so jinlyps, b, carries on the sides of its body two small ones which sprint: 

 from it, and will soon be detached. In Fijj. 3 (p. 19) may be seen one of these 

 animals magnified still more than the above, to show its internal confor- 

 mation. 



