488 SENSIBILITY AND MOVEMENTS OF HYDRA. 



observed that, as if excited by the injury, young Polypes sprout 

 more abundantly from the wounds thus made, than from un- 

 scarred parts. But even this is not all ; for two Polypes may 

 be grafted together by any parts ; and not only two of the 

 same species, but a green and a brown one may be thus 

 united. 



105 1 . The Polype does not seem to possess any special organs 

 of sensation, or to have any kind of feeling but that of touch. 

 It may be doubted, indeed, how far the greater part of its ac- 

 tions necessarily involve true sensation ; that is, how far it is con- 

 scious of the impressions which are made upon it, and to which 

 its organs respond. Many of its movements present considerable 

 analogy with those of Plants ; especially those of the Dioncea 

 (VEGET. PHYSIOL. 422). The Hydra generally seek the 

 light ; and, if a number of them be placed in a glass vessel, they 

 will cluster at the side on which it strikes. We have no reason 

 to suppose, however, that they are conscious of its presence as 

 light, since no rudiments of visual organs can be detected. It 

 would rather seem that it exercises an influence on their bodies, 

 which causes them to seek it, very much in the same manner 

 that Plants direct themselves towards it. The locomotive powers 

 of the Hydros are more exercised for this purpose than for the 

 search after food. When seeking their prey, they generally fix 

 themselves, by a kind of sucker at the lower end of the stomach, 

 to some solid body ; and their food is obtained by the tentacula 

 alone. When they desire to change their place altogether, they 

 do it in the manner of the geometrical Caterpillars ( 702), and 

 of some Leeches. If the foot or sucker be attached, the body is 

 bent until the head touches the surface, along which it intends 

 to move. It then adheres by the mouth, or by one or two of 

 the tentacula ; and, detaching the foot, draws it up into close 

 proximity with the head. The foot then takes a fresh attach- 

 ment ; and the head is projected forwards, fixes itself, and is 

 followed by the foot in the same manner as before. This mode 

 of progression is, from the minute size of the animal, necessarily 

 slow. A march of two inches occupies several hours for its per- 

 formance ; and seven or eight inches may be regarded as a very 



