ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
597 
( Paludina ), or rapidly become so, the left lobe being more developed 
than the right. In some cases ( Elysia , Avion , Buccinum) the adult 
exhibits an acquired, secondary, bilateral symmetry. 
In the number of the hepatic canals some Scutibranchs whose 
organization is very primitive (Fissurellidse) have three distinct hepatic 
canals. The same is true of some Opisthobranchs (. AEolis ) and some 
Pulmonata, in which the left lobe is divided into two distinct masses. 
It appears to be a primitive arrangement among Molluscs for the two 
hepatic lobes of the embryo to divide, during development, into several 
masses which open separately into the stomach. In consequence of a 
simplification of the embryogeny and a condensation of the hepatic organ 
this complete division is not found in the more differentiated forms ; 
but this apparent simplicity is no more primitive than the acquired 
symmetry already spoken of. 
The general modifications of the liver cannot serve as characters for 
the different classes of Mollusca, but they are useful as means by which, 
in the different classes, the most primitive types may be sought for ; the 
deductions from them agree with those drawn from the study of other 
organs. 
The variations of the liver and its ducts in the Prosobranchiata are 
well suited for a study of the variations seen in a given group, for they 
are very considerable. On the whole, it is clear that there is in them 
an evolution comparable to that of other organs, for the liver of the 
highest Pectin ibranchs is very different from that of the Scutibranchs 
or holostomatous Tsenioglossata. At the same time, it is not to be sup- 
posed that the divisions which can be established by the use of the liver 
are always the same as those to which other organs incline us. 
A slight comparison is instituted between the liver of Molluscs and 
that of some other Invertebrates. The liver of Brachiopods has exactly 
the same conformation and the same development as that of Lamelli- 
branchs. In the embryonic stages of the Bryozoa the appearances are 
the same as in Molluscs, though the adult condition is very different. 
Excretion in Pulmonate Gastropoda.* — M. L. Cuenot has improved 
on preceding methods of physiological injection by injecting into the 
coelom of various Gastropods peptonized solutions containing one or 
more of a rather large number of staining reagents. The health of the 
animal is in no way affected if the injection is properly performed ; the 
substances are very rapidly absorbed by the excretory cells, which are 
always contained in vacuoles. 
By means of this process the author has been able to recognize 
three different excretory organs — the kidney, certain cells of the liver, 
and the large vesicular cells of the connective tissue (Leydig’s cells). 
The vacuolated cells of the liver, which have been regarded as pro- 
ducers of ferment, are really excretory in function. The cells of Leydig 
are remarkable for the multiplicity of their functions. 
The renal cells which normally excrete uric acid and other pro- 
ducts have a very acid reaction, and the organ is certainly not an 
alkaline gland as Kowalevsky supposed. The part played by the 
liver of Pulmonata in excretion allies them to the Opisthobranchs, 
with which they have much in common. In Aplysia , Doris , and Eolis, 
* Comptes Rendus, cxv. (1892) pp. 256-8. 
