24 OX POLYPS. 



fluid mass, and the shell or hard integument is expelled through the 

 same aperture by which it entered the stomach. 



We will not even hazard a conjecture concerning the process by 

 which digestion is effected in this case, our knowledge of animal 

 physiology is by no means sufficiently advanced to render any 

 attempt at explanation useful ; we will rather pass on, and enquire 

 in what manner the nutritious parts of the food are conveyed into 

 the system of the polyp. We have already observed that no 

 traces of vessels of any kind have as yet been detected in the 

 granular parenchyma of which the creature seems to be 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 

 planarite, the granules of the body are seen to acquire a simi- 

 lar hue, but the fluid in which they float remains quite trans- 

 parent ; 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 which it has devoured; sometimes the granules thus 

 tinted are seen to be forced into the tentacula, from whence 

 they are driven again by a sort of reflux into the body, pro- 

 ducing a kind of circulation or rather mixing up of the granular 

 matter which distributes it to all parts. If, after having thus 

 digested coloured prey, the polyp is made to fast for some time, 

 the vesicles gradually lose their deepened hue and become com- 

 paratively transparent. The granules, therefore, would seem to 

 be specially connected with the absorption and distribution of 

 nutriment. 



(32.) Rapid as is the action of the stomach upon food introduced 

 into it, it has no effect upon other parts of the animal when immersed 

 in its cavity : the arms, for example, of the long-armed hydra are 

 frequently coiled around its prey during the process of its solution, 

 without receiving the slightest injury. This circumstance may 

 not appear very remarkable, but it has been found that other 

 polyps of the same species are equally able to resist the solvent 

 action. Trembley once saw a struggle between two of these 

 creatures which had seized upon the same animal ; both had partially 

 succeeded in swallowing it, when the largest put an end to the 

 dispute by swallowing its opponent as well as the subject of con- 

 tention. Trcmbley naturally regarded so tragical a termination 



