ORGANS OF NUTRITION.
The act of nutrition and its organs are objects of difficult observation in this series of animalcules, on account of the impossibility of using the means employed by Mr. Ehrenberg in the investigation of the true Infusoria, because the creatures, mentioned in this inquiry, do not admit colouring substances. Analogy alone can assist us, and even very weakly, in these researches.
In the Surirellae and Naviculae I could not discover any tnbe running parallel to the body.
We see, however, in the Surirella Venus a skin separating itself from one of the points of the coat, in which skin (d. fig. 4.) there is an incision, leading to the content (e). By means of this overture, the animalcule throws out entirely the content; but I never could distinguish upon the coat any opening nor fissure.
The Naviculae, according to my classification, include the species of the most ancient genera of Frustuliae and Naviculae; which, next to the pedal surfaces (fig. 4. 8. e.), found in the axe of the body, are supplied with two openings (d. d.) leading to two empty tubes (f. f.) passing through the whole animal, and, on both opposite extrmities, terminated also by two holes, near the smooth pedal surface.
In the Navicula costata (fig. 10.) these two openings are found under the flat pedal surface, and
