HYDKOZOA. 33 



the two parts will unite and form a perfect Polype 

 without leaving a scar. They may even be turned 

 inside out like a glove without injury, and in this 

 state will remain, that which was the external surface 

 now being the stomach. 



The ordinary mode of increase is by the young 

 animals budding from the side of the adult, but 

 previously to their separation, the offsets themselves 

 often send out side-buds, so that several generations 

 may sometimes be seen branching from one parent ; 

 nineteen young of various ages have been seen thus 

 connected, their numerous long tentacles twining 

 about in inextricable confusion. 



To the earlier observers of the habits of the Hydrae, 

 nothing could be more mysterious than their power of 

 seizing and retaining active prey ; but this is now 

 readily explained. The whole surface of their ten- 

 tacula is densely provided with a set of organs that 

 appear, under high powers of the microscope, to be 

 minute oval vesicles, something like little soda-water 

 bottles, in each of which is coiled up a long and 

 delicate filament, not unaptly compared to the lasso 

 used by Brazilian horsemen. 



The neck of each vesicle is furnished with three 

 sharp spines, which, when the arms are prepared to 

 seize the prey, become erect and prominent. The 

 mode of action of these weapons is as simple as the 

 result is efficacious. The " lasso-threads," with their 

 viscid extremities, speedily involve the seized victim 

 in their tenacious folds, and closely bind it against 

 the spines with which the skin of the Hydra is studded ; 

 these, probably, in their turn, become prehensile in- 

 struments ; and, moreover, apparently form an appa- 

 ratus of poison fangs of a very deadly character, for 

 it is observable that an animal once seized by the 

 Hydra, even should it escape from its clutches, almost 

 immediately perishes. 



We have dwelt at some length upon the history 

 of the Hydra, partly on account of the interest which 

 attaches to an animal so simple in its apparent 



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