of the Poly gastric Infusoria. 435 



CI. acerosum, which is figured in Plate IX. B. fig. 1. We see that 

 the animal, which is expanded in the middle, is elongated sym- 

 metrically on each side. In the middle there is a transverse fis- 

 sure m, which probably serves for the admission of nourishment ; 

 since, when this animal is kept for some time in coloured water, 

 we perceive little accumulations of the colouring matters. At the 

 extremities we see on each side a vesicle b, in which minute gra- 

 nules (?) incessantly move. In other species there is moreover a 

 small aperture r ; it is situated more posteriorly, and is perhaps 

 connected with the cell. Ehrenberg twice saw in this animalcule 

 filaments (feet ?) project from it. Internally there are, on each 

 side, two to four cords, s' s" s ,n , and a row (in other kinds several) 

 of glandular bodies d. In the species figured, I have so often 

 seen the above change in relative position, that I have been 

 compelled to wait until they again appeared in their original po- 

 sition in order to delineate them. All this is not plant-like ; and 

 if the carapace of the Closterina should prove to be of a horny 

 nature, as would appear to be the case from their becoming 

 wrinkled when heated, they would be removed from the vegetable 

 kingdom with still greater certainty. 



II. Bacillarina. — The greatest doubt has certainly been raised 

 regarding the animal nature of the forms which belong to this 

 family. I think however that if we collect all the observations 

 which have hitherto been made upon these bodies, they must be 

 referred to the animal kingdom. We will therefore consider the 

 following : — 



I have, a hundred times, seen Navicula Acus and Librile swim 

 against the current as distinctly as the Closteria, so that these 

 motions cannot be regarded otherwise than as dependent upon 

 the will of the animals. In addition to this, the shells of all the 

 Bacillarina are formed in a much more complicated manner (3) 

 than the other inorganic parts which we commonly find in plants. 

 We find calcareous incrustations, crystals, &c, but never such sym- 

 metrically formed shells as in the Bacillarina. Plants have no such 

 power over inorganic chemical agency as to elaborate inorganic 

 matters according to their will independently of the laws of such 

 matters, and such as we must presuppose to exist in the formation 

 of the carapace of the Bacillarina. The exsertion of feet at the an- 

 terior, and probably also at the inferior apertures of the carapace, 

 speaks decidedly in favour of the animal nature of the Navicula. 

 Ehrenberg first detected it, and described it in the * Transactions 

 of the Berlin Academy *. J After him it was observed by Schmidt, 

 and in the latter part of the autumn of last year I succeeded in 

 seeing it. Its not being more frequently detected, depends upon 



* For the year 1836, p. 134, and 1839, p. 102; and Taylor's Scientific 

 Memoirs, Parts X. and XI. 



212 



