coloured substance of these animalcules, which, surrounded with the coat, colours them in a particular manner. These substances appear to me in general gelatinous, half liquid, homogeneous, containing drops of oil or of fat, and very small solid grains.
In the Surirella Venus, this substance forms a brown or green mass (fig. 4. e.), heaped in the middle of the animalcule. In the Naviculae, the Frastuliae, and in some of the Diatomeae, this mass forms a small thin leaf, coloured, bent in its edges downwards, such as in the Frustulia appendiculata, (Pl. I. fig. 13. c. c.) which, when the animalcule dies, is irregularly dissolved. The genus Scalptrum and some species of non-described Naviculae, ean expell, without dying, the coloured content, through the opening found on the surface of the belly (Pl. V. fig. 70. b.) and these animalcules seem to possess the faculty of reproducing the content.
This content is equally seen in the Diatomeae and Fragilariae, and the two extremities of the body alone, being empty, are transparent. In the articulations of the Diatoma fenestratum, it merely consits in pale globules, always single and of various size (fig. 38.).
The genus Closterium, and those which are related to it, are on each side filled with a green substance, similar, though chemically different, to the chlorophylle of leaves: which substance covers large drops of a yellow oil (fig. 57. h. fig. 64. f.). This substance is here, as well as in the Frustuliae, intercepted in the middle of the body, and consequently divided
