306 . HYDRA CHAP. 



functions of baking and butchering are assigned to 

 certain members of the community, and not performed 

 by all. Hydra is therefore an example of individuation : 

 morphologically it is equivalent to an indefinite number 

 of unicellular organisms : but, these acting in concert, 

 some taking one duty and some another, form, physio- 

 logically speaking, not a colony of largely independent 

 units (compare p. 277), but a single multicellular 

 individual. 



Hydra has two distinct methods of reproduction, 

 asexual and sexual. 



Asexual multiplication takes place by a process of 

 budding. A little knob appears on the body (Fig. 7 

 A, bd l ), and is found by sections to arise from a group 

 of ectoderm-cells ; soon, however, it takes on the 

 character of a hollow outpushing of the wall containing 

 a prolongation of the enteron and made up of ecto- 

 derm, mesoglcea, and endoderm (Fig. 76, A, bd l ). In 

 the course of a few hours this prominence enlarges 

 greatly, and near its distal end six or eight hollow buds 

 appear arranged in a whorl (Figs. 75, A, and 76, A bd 2 ). 

 These enlarge and take on the characters of tentacles, 

 and a mouth is formed at the distal end of the bud, 

 which thus acquires the character of a small Hydra 

 (Fig. 75, A, bd 3 ). Finally the bud becomes constricted 

 at its base, separates from the parent, and begins an. 

 independent existence. Sometimes, however, several} 

 buds are produced at one time, and each of these buds 

 again before becoming detached : in this way temporary 

 colonies are formed. But the buds always separate 

 sooner or later, although they frequently begin to feed 

 while still attached. 



It is a curious circumstance that Hydra can also be 

 multiplied by artificial division : the experiment has 



