138 
MOLLUSCA. 
invagination, filled with a brownish viscid mass, which, spreading out 
afterwards, gives origin to the external shell. The walls of the internal 
cavity of the embryo give direct origin to the stomach and intestine. 
The branchial cavity is a depression of the ectoderm. C. K. Ixxxi. p. 472 
et seq. ; abstract in Ann. N. H. (4) xvi. pp. 435-437. 
E. Ray Lankester publishes some observations on the development 
of Paludina vivipara, stating that the orifice of the embryonal invagi- 
nation by which the alimentary canal is formed, remains open as the 
anus ; whereas it closes in other Mollusca, as for example, Pisidium^ 
Limncuay and the Nudihranchia. This orifice may be called blastopore. 
Q. J. Micr. Sci. (2) xv. pp. 169-163, and xvi. pp. 377-385, pi. xxv. 
H. Fol’s researches on the development of the Pulmonate Gastero- 
poda lead him to the conclusion, that it resembles in many points that of 
the Heteropoda ; in all, there is total segmentation, the nutritive half of 
the yelk becomes invaginated, the aperture of the invagination or the 
primitive mouth does not become the anus, as Lankester asserts, the 
dorsal projection at the primitive mouth enters by degrees into the oeso- 
phagus, and has nothing in common with the velum of the marine 
Qastropods, as Ihering asserts, but a true velum exists in all the aquatic 
Pulmonata as a zone of cilia interrupted on the back, and in Helix as 
two ciliated crescentiform ridges. The primitive kidney occurs also in 
the aquatic Pulmonata^ and is in its 'origin a depression of the ectoderm ; 
it has been misunderstood by Rabl and Ganin. The foot of the aquatic 
Pulmonata contracts alternately with the neck, thus producing a larval 
circulation ; in the terrestrial Pulmonata^ the extremity of the foot be- 
comes*converted into a great contractile vesicle, which contracts alter- 
nately with the dorsal vesicle. C. R. Ixxxi, p. 623 et seq. ; abstract in 
Ann. N. H. (4) xvi. pp. 375 & 376. 
The development of Helix pomatia and nemoralis is discussed by H. v. 
Ihering j he describes a rudimentary velum provided with vibratile 
cilia in the embryo, stating that the shell is internal on its first appear- 
ance, and therefore homologous to the little internal plate of Limax 
(contrary to Ray Lankester’s opinion). He mentions the [well known] 
constant correlation of the side in which the genital and anal orifices are 
situated, with the direction of the whorls of the shell, and declares the 
embryonal caudal vesicle to be a respiratory organ ; the foot of Helix is, 
according to this author, essentially a propodium, in the sense proposed 
by Grenacher [see Zool. Rec. xi. p. 117] ; peculiar attention has been 
given to the nervous and genital systems, the author thinking that the 
pallial ganglion is homologous to the ventral chain of ganglia in the 
Vermes^ and that the pedal ganglion has no homologies with them, 
whereas Gegenbaur and others regard the pedal ganglion as homolo- 
gous to the ventral chain and the pallial ganglion to be a part of the 
sympathetic system. In the genital system he describes a small seminal 
vesicle, belonging to the male apparatus, situated near the origin of the 
albuminous gland ; as to the place in which the eggs are fecundated, he 
agrees with Perez [see Zool. Rec. x. p. 155] that it is not at the base of 
the stalked vesicle, or female receptaculum seminis, but considerably 
higher up. Jen. Z. Nat. ix. 42 pp. pis. xvii. & xviii. 
