NUTRITION IN POLYPI. 71 



those of every subsequent observer have farther 

 contributed to confirm. 



The experiments of Trembley have also proved 

 that every portion of the hydra possesses a wonder- 

 ful power of repairing all sorts of injuries, and of 

 restoring parts which have been removed. These 

 animals are found to bear with impunity all kinds 

 of mutilations. If the tentacula be cut off, they 

 grow again in a very short time; the whole of the 

 fore part of the body is, in like manner, reproduced, 

 if the animal be cut asunder ; and from the head 

 which has been removed there soon sprouts forth a 

 new tail. If the head of the hydra be divided by 

 a longitudinal section, extending only half way 

 down the body, the cut portions will unite at their 

 edges, so as to form two heads, each having its 

 separate mouth, and set of tentacula. If it be split 

 into six or seven parts, it will become a monster 

 with six or seven heads ; if each of these be again 

 divided, another will be formed with double that 

 number. If any of the parts of this compound 

 polypus be cut off, as many new ones will spring 

 up to replace them ; the mutilated heads at the 

 same time acquiring fresh bodies, and becoming as 

 many entire polypi. Fig. 245 represents a hydra 

 with seven heads, the result of several operations 

 of this kind. The hvdra will sometimes of its own 

 accord split into two ; each division becoming inde- 

 pendent of the other, and growing to the same 

 size as the original hydra. Trembley found that 

 different portions of one polype might be engrafted 

 on another, by cutting their surfaces, and pressing 

 them together ; for by this means they quickly 

 unite, and become a compound animal. When 



