Form of Freshwater Coelenterate. 119 



example in the form B, may all be replaced by new ones, 

 which sprout forth in the same number, of the same structure, 

 and at the same place as the old ones. Thus, for exam])le, 

 the tentacles of a Polyjpodium in stagnant and somewhat 

 tainted water die off and become macerated down to their 

 roots. We have only to place an animal thus mutilated (the 

 generation is of no consequence) in fresh flowing water in 

 order to see how, within only a few hours, small tubercles are 

 formed in the places of the old tentacles, and these in three or 

 four days grow into tentacles nearly of the normal length 

 (five or six times the length of the body). During this process 

 of reproduction of new tentacles the body proceeds to divide ; 

 thus, for example, a mother B and even «B divided, after a 

 horseshoe-shaped constriction, into the daughter-forms B^ and 

 «B^ with twelve tentacles. 



I pass now to the description of the external form and 

 structure of the body in the mother-, daughter-, and grand- 

 daughter-generations. 



I have already shown that, parallel with the gradual deve- 

 lopment of the parasitic generation, the pyriform body of the 

 secondary buds {b) acquires a trapezial form by flattening in 

 the transverse axis, with a groove at the upper and a peduncle 

 at the lower end. 



On the breaking up of the stolo the liberated buds, by the 

 deeper impression of the transverse furrow, acquire the form 

 of a horseshoe, the two arms of which terminate in cubical 

 enlargements. Provided with a small fragment of the stolo 

 and at first with a common peduncle, the buds, which separate 

 in pairs, after definitive isolation acquire a conical proboscis 

 with a transverse buccal fissure. Upon each of the two sides 

 of the horseshoe there originate twelve tentacles, three pairs 

 on each of the shoulders and three pairs at the free extremities 

 on each side of the furrow (^ - 24) . The tentacles in each 

 of these four regions of the body may be divided into a pair 

 of feelers and two pairs of radial tentacles. I employ 

 the latter expression for the sake of brevity ; they originate 

 with a common base and diverge radially, and are thinner, 

 longer, and much less sensitive than the feelers, which bear 

 nettling batteries at their extremities. 



After the division of the mother- form each daughter acquires 

 half the tentacles (^-^=12). In the same way there come to 

 each of the grandchild-forms, after the division of the daughters, 

 six tentacles (1^ = 6), two pairs of radial tentacles, and one 

 pair of feelers. Thus we obtain from each side of the 

 liorseshoe-shaped generation B a form B^, and this again 



