2 MECHANICAL FUNCTIONS. 



complete animal. If the head of the Hydra and a por- 

 tion of the body be divided by a longitudinal section, 

 the animal is thereby the gainer, for the divided parts 

 form two heads instead of one, with complete sets of 

 tentacula for each mouth, and thus he can enjoy the sat- 

 isfaction of eating with two mouths at the same time. 

 If the head be split into half a dozen parts, each part will 

 form a new head with mouth and tentacula to match, 

 Fig. 11. the whole being united to one body. 

 Fig. 11 represents a seven headed 

 monster, the result of several mutila- 

 tions and divisions of one of these pro- 

 tean creatures. 



Sometimes of its own accord a Hy- 

 dra will split in two parts lengthwise, 

 each division becoming independent of the other, and 

 growing to the same size, and attaining the same organs 

 as the original animal. 



Mr. Trembley also found that any portion of one 

 Hydra might be engrafted on another, in the same man- 

 ner that pieces of India rubber may be joined, that is, 

 by cutting their surfaces and pressing them together. 

 By this means they would unite and become a compound 

 animal. Thus many heads may be united to one body, 

 or many bodies to one head ; and so on the contrary 

 when one Hydra is introduced into the mouth of another 

 so that their heads are kept in contact, for a time, they 

 unite and become one individual animal. 



Even the figures of other animals, as quadrupeds, or 

 man, might be constructed in this manner, though every 

 where covered with moving tentacula. 



PENNATUL.E. 



Another form under which polypi exist, is that called 

 Pennatula. This is called sea pen, from its re- 



How may parts of these animals be engrafted upon each other? 

 some account of the pennatulae. 



