ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
589 
whose secretion digests starch and cellulose ; ( b ) absorptive cells ; and 
(c) lime-cells. In the absorptive cells and lime-cells glycogen is stored, 
and fat, and perhaps some albuminoids. The lime-cells have especially 
to do with fat-storage, and they also contain calcium phosphate. The 
fresh secretion has no appreciable effect on albuminoids. 
No food is absorbed in the intestine, which is lined by ciliated and 
glandular cells. From the stomach the fluid food passes into the gastric 
gland, whence some of it passes back in altered form. 
Anatomy of Neritina fluviatilis.* — Dr. Lenssen points out the 
difference of opinion which exists in text-books as to the characters of 
the nervous system in this mollusc. He has studied it by the method 
of sections, and finds that Neritina belongs to the Ohiastoneura, but 
displays either an initial or a regressive form of this condition. As to 
the heart, Lenssen finds that one auricle only is present. The nephri- 
dium has the ordinary structure. It consists of a tube bent on itself, 
and thus forming two chambers. Of these the upper has greatly folded 
walls, and opens by a ciliated nephrostome into the pericardium, while 
the lower has smooth walls, and opens into the branchial cavity. The 
rectum passes through the ventricle. 
Development of Paludina vivipara.f — Herr C. Tonniges has re- 
peated his former observations on this subject, and finds that his renewed 
research confirms his previous assertion that the mesoderm originates, 
not from primitive mesoblasts or coelom sacs, but by the migration of 
ectoderm cells on the ventral surface of the embryo. In the cell-masses 
formed by the proliferation of the ectoderm cavities appear, which form 
the coelom or pericardium. On the ventral wall of this primitively 
double cavity two thickenings appear, which are the primordia of the 
nephridia. Of these the left aborts. The originally paired ureter arises 
as an outgrowth of the mantle-cavity. The heart arises from a folding 
of the dorsal wall of the pericardium ; the blood-vessels as spaces in the 
mesenchyme. The mesenchyme*, like the mesoblast, arises from ectoderm 
cells, so that in Paludina all the cells lying between ectoderm and endo- 
derm originate from the former. 
Development of Chiton4 — Mr. Harold Heath publishes an elaborate 
paper on the natural history, breeding habits, and development of Ischno- 
chiton magdalenensis , and adds to his paper a discussion of cell-homologies 
between Annelids and Mollnsca, and of the primitive form and relations 
of the trochophore. The Chiton studied is remarkable in laying its 
eggs in jelly masses instead of singly, the egg-strings having an average 
length of 31 inches, with an average content of 115,940 eggs. The larvae 
begin to rotate in their egg-membranes at the end of 24 hours ; six days 
later they begin their brief free-swimming existence, and after at the 
most a couple of hours, settle down on rocks and seaweeds, and undergo 
a gradual process of metamorphosis. The cleavage is total and nearly 
equal ; the early cleavages conform to the radial type, and traces of 
radial symmetry persist until the close of the free-swimming life. 
* Anat. Anzeig., xvi. (1899) pp. 401-4. 
t S.B. Ges. Naturwiss. Marburg, 1899, pp. 1-10. See Zool. Centralbl., vi. (1899) 
pp. 702-5. 
t Zool. Jahrb. (Abt. Anat.), xii. (1899) pp. 567-656 (5 pis. and 5 figs.). 
1899 2 r 
