306 HYDRA CHAR 



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. 75^ 

 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, mesogloea, 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 s ). 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 



