20 ZOOLOGY. 



mouth to the vent, v/hich he regards as so many stomachs. This view 

 passed undisputed for a considerable time ; for although other observers 

 failed to detect the connexion between tlie supposed stomachs and intestine, 

 the failure was attributed to want of skill in microscopic manipulation. 

 Ultimately this structure was doubted, although Pouchet reaffirmed it in 

 1848, and among others, Professor Rymer Jones expresses his doubts as 

 follows : 



" In carnivorous animalcules which devour other species, we might expect, 

 were these the stomachs, that the prey would at once be conveyed into one 

 or other of these cavities ; yet, setting aside the difficulty which must mani- 

 festly occur in lodging large animalcules in these microscopic sacs, and 

 having recourse to the result of actual experience, we have never in a single 

 instance seen an aninuilcule, when swallowed, placed in such a position, but 

 have repeatedly traced the prey into what seemed a cavity excavated in the 

 general parenchyma of the body. 



" In the second place, the sacculi have no appearance of being peduncu- 

 lated, and consequently in a certain degree fixed in definite positions. . . 

 So far from their having any appearance of connexion with a central canal, 

 they are in continual circulation, moving slowly upwards along one side of 

 the body, and in the opposite direction down the other, changing, moreover, 

 their relative positions with each other, and resembling in every respect the 

 colored granules visible in the gelatinous parenchyma of the hydra. 



" With respect to the central canal, we have not in any instance been 

 able to detect it . . . much less the branches represented as leading from it 

 to the vesicles or stomachs, as they are called. Even the circumstances 

 attending the prehension of food would lead us to imagine a different 

 structure ; witness, for example, the changes of tbrm which Enchelis pupa 

 imdergoes when taking prey almost equal to itself in bulk. Such a capability 

 of taking in and digesting a prey so disproportionate, would, in itself, go far 

 to prove that the minute sacculi were not stomachs; as it evidently cannot 

 be in one of these that digestion is accomplished." — General Outline of the 

 Aiiimal Kingdom^ 1841. 



The observations of Dujardin (llist. nat. des Zooph. Infusoires, 1841) 

 confirm those of Jones, He thinks that they do not lay eggs. 



Many of Ehrenberg's discoveries were made by infusing indigo or carmine 

 in the water in which he kept Infusoria, and this being swallowed, marked 

 the limits of the internal cavity. He did not detect the liver, spleen, or 

 organs of circulation and respiration ; but there are two organs in the gullet 

 supposed to be analogous to salivary glands. 



All Infusoria live in the water, some beijig confined to fresh, and others 

 to salt water; but there are others which inhaljit both. Some swim about 

 almost continually, some attach themselves at will to plants or animals, and 

 others are attached to particular animals, as to the C)jdops or waterflea, the 

 freshwater Polypus ; and even upon or within other Infusoria. One species 

 is found in the rectum of frogs, and another {Paramecium oompressum) in 

 the intestines of the earthworm. Agassiz has observed the eggs of Planaria 

 producing a species of " Paramecium'''' which was consequently an immature 

 condition of that animal. All the attempts of Ehrenberg to detect Infusoria 

 as inhabitants of the air have failed. * 



224 



