HYDRA VIEIDIS. 8t 



(180.) To the earlier observers of the habits of the Hydra nothing 

 could be more mysterious than this faculty, possessed by the creature, 

 of seizing and retaining active prey, in spite of all its efforts at resist- 

 ance, but which is now satisfactorily explained as depending upon the 

 presence of a prehensile apparatus, allied in its nature to the filiferous 

 capsules of the Actinice, described in the last chapter. These wonderful 

 organs are not only thickly dispersed over the whole surface of the 

 tentacles, but are likewise met with, though less numerously distributed, 

 over the general surface of the body. They appear, under high powers 

 of the microscope, to be composed of minute oval vesicles, from each of 

 which can be protruded a long delicate filament, having its free ex- 

 tremity slightly swollen, and apparently of a soft viscid texture, the 

 whole being not inaptly compared by Agassiz to a lasso. The neck of 

 each vesicle is furnished with three recurved booklets, which, when 

 the skin of the animal is irritated, or when the arms are prepared to 

 seize prey, remain erect and prominent. The modus operandi oi^ these 

 structures is as simple as the result is efficacious : the " lasso-threads" 

 with their viscid extremities, speedily involve the victim seized, in their 

 tenacious folds, and closely bind it against the booklets wherewith the 

 surface of the tentacula is thickly studded : these, probably, in their 

 turn constitute prehensile organs, and moreover form an apparatus 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. 



(181.) Arrived in the stomach of the polyp, the animal that has 

 been swallowed is still distinctly visible through the transparent body 

 of the Hydra, which seems like a delicate film spread over it (fig. 39, 4) ; 

 gradually the outline of the included victim becomes indistinct, and the 

 film that covers it turbid; the process of digestion has begun: the 

 soft parts are soon dissolved and reduced to a fluid mass, and the shell 

 or hard integument is expelled through the same aperture by which it 

 entered the stomach. 



(182.) No traces of vessels of any kind have as yet been detected in 

 the granular parenchyma of which the creature is composed ; coloured 

 globules are seen floating in a transparent fluid, which, in the Hydra 

 viridis, are green, although in other species they assume different tints. 

 When the food has been composed of coloured substance, as, for example, 

 red larvae, or black Planarice, the granules of the body acquire a similar 

 hue, but the fluid wherein they float remains quite transparent ; each 

 granule seems like a little vesicle into which the coloured matter is 

 conveyed, and the dispersion of these globules through the body gives 

 to the whole polyp the hue of the prey it has devoured ; sometimes the 

 granules thus tinted are forced into the tentacula, from whence they are 

 driven again by a sort of reflux into the body, producing a kind of cir- 

 culation, or rather mixing up, of the granular matter, and distributing it 



