ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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metrical nerve-centre (centre asymetrique), and to name its constituents 
from their position (right lateral, left lateral, &c.). This is justified 
first by the fact that the want of symmetry in this centre is eminently 
characteristic of Gasteropods, and second, by the fact that there is not 
constancy in the regions innervated by the individual ganglia. Thus 
the ganglia called pallial do not always send nerves to the pallium. 
These statements are proved by a series of dissections and drawings of 
the nervous system in different Gasteropods. 
Anatomy of Acmaea fragilis.* — Mr. M. A. Willcox has made a 
detailed study of this New Zealand mollusc. The following are the 
most generally interesting of his observations. The visual organs are 
pigment-lined pits, apparently capable of contraction and expansion. 
It is probable that the pigment-cells, as in the Cephalopoda, are capable 
of some movement, but to a much lesser extent. The heart has only one 
auricle, the primitively left being only occasionally represented by a 
rudiment. The ventricle is not divided into two chambers as in Patella. 
The gill consists of two series of transverse lamellae, and the mantle also 
acts as a respiratory organ. There is no true coelom, but a large blood- 
carrying space represents the “ primary body-cavity.” One nephridium 
only is present, and the animals are bisexual, but owing to the marked 
protandry the hermaphrodite state is of very brief duration. The paper 
is furnished with a very complete bibliography. 
Cellulose-dissolving Ferment in Snail.f — Herren W. Biedermann 
and P. Moritz have shown experimentally that the cell-walls of many 
parts of plants — grain of wheat, potato tuber, date endosperm, &c., dc. — • 
are dissolved much more quickly than the starch-grains by the secretion 
of the digestive gland of Helix pomatia. The cellulose-dissolving 
ferment was not isolated, but its existence seems securely established. 
Development of Tethys fimbriata.J — Dr. Camille Viguier has at 
various times succeeded in obtaining developing eggs of this Opistho- 
branch, and publishes some observations on the development. Tbe 
spawn takes the form of a flattened helix, and the eggs are enveloped in 
a large amount of glairy substance which is later in large part absorbed 
by the larvae. The eggs are quite opaque, being filled with rose-coloured 
volk-spherules. They segment completely, two perfectly equal blastc- 
meres being formed in each egg. These blastomeres do not, however, 
segment simultaneously ; one always lags behind the other, so that one 
side of the egg may consist of macromeres and micromeres, while the 
other shows still the undivided blastomere. This was also observed by 
Heymons in Umbrella. The author believes it to be the primitive 
method, and the one which furnishes the best explanation of the ordinary 
position of the four blastomeres of the second generation. The origin 
and fate of the macromeres and micromeres are considered in detail, and 
the results compared with those of Heymons in the case of Umbrella. 
* Jenaische Zeitschr. Naturwiss., xxxii. (1898) pp. 411-56 (3 pis.).* 
f Arch. ges. Physiol., lxxiii. (1898) pp. 219-87 (2 pis.). See Tot. Ztg., lvii. 
(1899) (2 te Abth.) pp. 18-9. 
, % Arch. Zool. Expe'r., vi. (1898) pp. 37-62 (3 pis.). 
