ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 313 
of the geological age, geographical distribution, hypsometric relations, 
and colouring of the Pulmonates, and with a distributional list of the 
western species. 
Development of Bythinia.* — Dr. R. v. Erlanger has followed the 
development of Bythinia tentaculata , and found that it does not differ 
essentially from that of Paludina previously described by himself. 
The segmeutation is the same as that of almost all the other Gastropoda 
which have been carefully studied, e.g. as regards the primitive meso- 
derm-cell. There is a typical invaginate gastrula, like that of Planorbis. 
A number of stages, which are figured, are described, showing the deve- 
lopment of the external form. 
A solid mass of mesoderm-cells acquires a lumen and becomes con- 
nected with an ectodermic duct to form the primitive kidney. There is 
no trace of internal aperture. An accumulation of mesoderm-cells in 
the region in front of the gut-rudiment forms the common basis of heart- 
chamber and kidney, which develope together. The heart arises as a 
groove-like invagination of the pericardial wall. The two cerebral 
ganglia originate separately in the ectoderm ; the pallial ( = pleural) 
ganglia also arise apart from one another, and apart from the cerebrals, 
as ectodermic proliferations, lateral and ventral to the velum and tentacle- 
rudiments ; pedal, intestinal, and visceral ganglia also arise apart. These 
results are in contradiction to those of Sarasin, from whom indeed in 
most respects Erlanger differs. The importance of the paper is mainly 
its corroboration in Bythinia of what the author previously observed in 
Paludina. 
Some Means of Defence in Eolididse.t — M. E. Hecht concludes, from 
his observations of stained preparations of the papillm of Eolis glauca , 
that the nematocysts contain a substance analogous to the contents of 
the mucous cells of epithelium, the fundamental constituent of which is 
probably mucin. By means of serial sections it is possible to follow 
without interruption the lumen of a well-marked canal, invested by a 
very distinct epithelium, which establishes communication between the 
cnidophoral sac and the hepatic caecum. It follows, therefore, that the 
digestive-tube of these Molluscs does not only communicate with the 
exterior by means of the mouth and anus, but also by as many small 
orifices as each individual has papillae. It is not in all, but only in 
some species that the dorsal appendages are easily detached. Most, 
and especially Eolis papillosa, preserve their papillae, notwithstanding 
varied and repeated stimuli. The rare Calma glaucoides has no trace 
of a cnidophoral sac, though the papilla is well formed. This want 
appears to be due to degeneration, as the sacs are possessed by an allied 
species ; the cause is, perhaps, to be found in the fact that this species, 
unlike most of its kind, does not feed on Coelentera. 
Structure of Proneomenia.J — Herr J. Heuscher has investigated 
Proneomenia Sluiteri Hubrecht, of which only a few specimens have as 
yet been found. The animal is like a short, thick worm, 75-98 mm. in 
length, its skin is rough and stiff with calcareous spicules, a ventral 
* MT. Zool. Stat. Neap., x. (1892) pp. 376-407 (2 pis.). 
t Comptes Rendus, cxv. (1892) pp. 746-8. 
X Jenaische Zeitschr. f. Naturwiss., xxvii. (1893) pp. 477-512 (4 pis. and 4 figs.). 
