remains always almost the same. Diving downwards and upwards, they move in circular lines, as molecules do. In the Closterium Lunula, several are often found; in the Closterium costatum, never more than one; in the Closterium didymotocum we see two twin globules (fig. 65. e.), forming only one body, the union of which is still visible.
In a series of species of this genus, I have seen, globules without apparent bladder, moving freely towards the empty point of the valvules: which motion is distinctly seen in the Closterium acuminatum (fig. 59. e.). The vesicle surrounds the coat contiguous to the cuirass, and that coat cannot be separated from it but by galvanic strokes.
When the Closteria die, these animalcules retreat downwards, and present nothing more than a scarcely visible spot. In squeezing them under a flat and very thin bit of glass, I sometimes succeeded in obtaining them single, and then they appeared to me quite spherical, without the least mark of adhesion. In the Closterium Lunula and didymotocum, we discover under the rotatory bladder, and above the first, the marks of an intestinal tube in right line (e. e.), surrounded with the green substance, which fills the animalcules. In spite of the finest instruments and innumerable trials, I never succeeded in separating this tube, because the green substance, half liquid, mixed with large oily drops, cover the whole, and baffles every direct observation.
Speaking of the intestines, we must mention the
