The Cosmarium deltoïdes (fig. 18-19) has two warty cuirasses, united on their broad surface, the openings of which communicate only with the surface uniting both animalcules. The Cosmarium bipes (fig. 20) has a cuirass of the same form, and appears however always split on its external surface, the more so as, during fecondation, this fissure (fig. 20. a. a) opens itself. In the middle of the lines which unite the two cuirasses of an animalcule, we see a nearly quadrangular opening of the uniting points; which opening is the mouth. On both sides of it are two openings (fig. 20. b.), through which the animalcule pushes a scarcely perceptible bladder, by means of which it sticks to the inside of the glass. I name therefore these openings pedal holes.
In the Colpopelta viridis (fig. 28) we see, on the inferior surface of the univalve cuirass two openings (a), placed opposite one another, which must be considered as those of the alimentary tube.
I name coat the epidermis which surrounds entirely the animalcule; and, as far as I could observe it in some larger species of Naviculae, inhabitants of rivers, that coat is, at the same time, the pedal organ, which, under a vesicular form, passes through the valvular openings, and by means of these feet the animalcule adheres to the glass.
In the cuirassed animalcules (such as the various species of Surirella, Navicula, Closterium and Cosmarium), the epidermis clothes the whole internal surface of the cuirass, and lines it like a bag.
