230 HYDRA 



ticular functions are made over to particular individuals- 

 just as in a civilized community the functions of baking and 

 butchering are assigned to certain members of the commu- 

 nity, and not performed by all. Hydra is therefore an ex- 

 ample 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, 

 they form, physiologically speaking, not a colony of largely 

 independent units, but a single multicellular individual. 



Like so many of the organisms which have come under 

 our notice, 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. 51, A, bdl\ and is 

 found by sections (Fig. 52, A, bd l ) to be a hollow out- 

 pushing of the wall containing a prolongation of the 

 enteron, and made up of ectoderm, mesogloea, and endo- 

 derm. In the course of a few hours this prominence en- 

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

 buds appear arranged in a whorl (Fig. 51, A, bd^ Fig. 52, 

 A, bd' 2 ). These enlarge and take on the characters of ten- 

 tacles : a mouth is formed at the distal end of the bud, 

 which thus acquires the character of a small Hydra (Fig. 

 51, A, M 3 ). Finally the bud becomes constricted at its base, 

 separates from the parent, and begins an independent ex- 

 istence. 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 mul- 

 tiplied by artificial division : the experiment has been tried 



