582 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
plate flattened dorsoventrally and divided by a constriction into an 
upper and a lower mass. 
The gonads are two long tubes with proper and continuous walls ; in 
their lower part they gradually acquire a common envelope which is at 
first connective and then muscular, and which also incloses the dorsal 
sinus. They, like the pericardium, have no relation with the general 
cavity, and like it, do not contain a single blood-cell. The pericardium 
is lined by a pavement epithelium, which is continuous and forms on the 
sides two longitudinal folds, where the cells become higher, cubical and 
ciliated. 
The author concludes that the so-called heart is not a propelling 
organ, as it is often devoid of a cavity, and never has contractile 
elements ; morphologically it is a mere dorsal raphe, a continuation of 
the septum of the gonad which becomes incomplete and incloses a 
portion of the general cavity ; physiologically, it aids in forming, on 
each side, with the lateral ciliated folds of the pericardium, a groove 
such as that which is seen at the end of the gonad of hermaphrodite 
Gastropods, and it is destined, like it, to separate the male and female 
elements which have hitherto been mingled with one another. The 
spormatozoa are conveyed into a special portion of the nephridial tubes, 
or into two long seminal vesicles, while the ova pass from the groove 
and accumulate in the so called pericardium ; this last is nothing more 
than an accessory pouch of the genital apparatus. 
The so-called nephridial tubes are simple genital ducts which have 
neither renal function, since their epithelium is not glandular, nor the 
value of segmental organs, since they do not communicate with the general 
body-cavity ; in fact, the genital apparatus, as a whole, recalls most 
nearly that of hermaphrodite Gastropods, with the difference that, in the 
Neomeniee, all the parts are paired and symmetrical. 
5. Lamellibranchiata. 
Identity of Composition of Nervous System of Lamellibranchiata 
and other Molluscs.* — M. P. Pelseneer points out that in most Mollusca 
each pedal ganglion receives two connectives — the more ventral or more 
anterior, which comes from the cerebral ganglion, and the more dorsal 
or posterior, which arises from the pleural ganglion. This arrangement 
is general in Gastropods, and has been found also in Cephalopods and 
in Dentalium. The absence, in Lamellibranchs, of the pleuro-pedal 
connective and of a distinct pleural ganglion have been regarded as 
definitely characteristic of the class ; however, in Nucula and Solenomya , 
more piimitive genera which M. Pelseneer has united under the group- 
name Protobranchiata, the pleural centres and the pleuro-pedal con- 
nectives are to be found. In Nucula the cerebral ganglia occupy the 
usual position, above the oesophagus ; they each give off fibres which 
pass to the adductor muscle and to the palps, as well as the connective 
which unites the cerebral centre to the corresponding pedal ganglion. 
More posteriorly, at the point where, as a rule, the visceral commissure 
commences, there is a ganglion which is as large as the cerebral ; this 
gives off the visceral commissure posteriorly and the anterior pallial 
Comptes Rendus, cxi. (1890) pp. 245-6. 
