670 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
in the development of Physa heterostropha, tlie adult of wliicli has a 
sinistral shell, and of Limnsea columella , whose shell is dextral. The 
type of cleavage in these eggs is spiral, but that of Physa is totally 
reversed. The first evidence of variation appears at a late ‘2-cell stage. 
Here the spiudles for the next cleavage, instead of being inclined from 
left below to right above, as they are in Limnsea , are inclined from right 
below to left above. This total reversion brings about in the 4-cell 
stage the reversion of the cross-furrows. 
The author does not seem to think that an immediate answer can be 
given to the question whether there is any correlation between the sinis- 
tral shell of the adult Physa and the unique method of cleavage. 
Experimental Nanism.* * * § — M. H. de Varigny has repeated and 
extended the late Prof. Semper’s observations on reduction of size in 
Limnseas auricularis and L. stagnalis. He comes to the conclusion that 
the favourable influence of large volume is not due, as Semper supposed, 
to the presence in the water of a chemical constituent which favours 
growth, but that {< nanism ” is due to want of activity and movement. 
Function of Kidney of Helix.f — M. L. Cuenot finds that if Snails 
or Slugs are kept in captivity they get rid of masses formed entirely of 
uric concretions, and exactly similar to those contained in the renal cells. 
In other words, the renal concretions of these animals are eliminated as 
such and not altered on their way out. A fortnight may elapse between 
two successive evacuations of these deposits. 
Branchiate Pulmonates.J — Dr. P. Pelseneer has discovered among 
the aquatic Pulmonates of Madagascar a sinistral form which is 
normally possessed of a well-formed gill ; this gill is folded and not 
pectinate, and is fixed by its base only ; it is not the homologue of the 
ctenidium of other Gastropods, for it is placed quite outside the pallial 
cavity ; it is, in fact, a new structure. 
A study of Belgian forms shows that there are signs of a like organ 
in Planorhis and Ancylus ; P. corneus has, outside the lung cavity, a 
flattened tegumentary lobe, the structure of which shows its respiratory 
function ; a similar, but smaller, lobe is present in P. marginatus. 
Ancylus , which has no lung at all, has the same lobe. The facts that 
the structure is a neomorph, and that the Pulmonata generally have lost 
their original ctenidium, afford an interesting example of the impossibility 
of a lost organ reappearing. 
The Madagascar form which has been called Physa lamellata is the 
type of a new genus which the author proposes to call Pulmobranchia. 
Notes on Polyplacophora.§ — Herr B. Haller describes some points 
of interest in the large Chiton magnijicus which he regards as a primitive 
species. The most interesting fact is that this species has four pairs of 
auricular openings into the ventricle, while other (younger) forms have 
two pairs, and some only one pair. This is a further argument in 
support of Gegenbaur’s view that the heart of Molluscs might be derived 
* Journ. Anat. et Physiol., A. 1891, pp. 147-88 (36 figs.). See Zool. Centralbl., 
i. (1894) pp. 513 and 4. 
t Comptes Rendus, cxix. (1894) pp. 339 and 40. % Tom. cit., pp. 354 and 5. 
§ Morphol. Jahrb., xxi. (1894) pp. 28-39 (1 pi.). 
