58 POLYGASTRICA. 



sacs, and having recourse to the result of actual experience, we 

 have never in a single instance seen an animalcule, 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 

 pedunculated, and consequently in a certain degree fixed in defi- 

 nite positions : during the last two hours we have been carefully 

 examining some beautiful specimens of Paramecium aurelia, 

 (Jig- 18, 4,) an animalcule which, from its size, is peculiarly 

 adapted to the investigation of these vesicles ; and so far from 

 their having any appearance of connection with a central canal, as 

 represented in the figure copied from Ehrenberg, they are in con- 

 tinual 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 coloured granules which have been described 

 ( 31,) as visible in the gelatinous parenchyma of the hydra. 



With respect to the central canal, (Jig. 18 ; , 3, 4,) we have 

 not in any instance been able to detect it, or even any portion of 

 the tube seen in the figures, 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 form which Enchelis pupa undergoes when taking prey, 

 as shown in fig. 16, 3, where it is represented in the act of devour- 

 ing a large animalcule, almost equal to itself in bulk, and is seen to 

 assume a perfectly different shape as it dilates its mouth to receive 

 the victim, with which its whole body becomes gradually distended. 

 Such a capability of taking in and digesting a prey so dispropor- 

 tionate, 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. 



(82.) Looking at the above facts as a whole, we cannot mistake 

 the analogy which there is between the organization of the so- 

 named Polygastrica and of the Hydra viridis ; there is the same 

 dilatable body in which the solution of food takes place, and the 

 same granular vesicles by which the nutritious portions are ab- 

 sorbed : that the vesicles become coloured by the coloured food 

 given to the animalcule, cannot be considered as a proof of their 

 being stomachs, as in the experiments of Trembley, above nar- 



