668 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
observations show that the worm really steals the hermit-crab’s food, 
and that it does not feed on faeces of its host. Nereilepas then is a 
true parasite and not a commensal. Pinnotheres, which has been thought 
to be a commensal of Lamellibranchs, is also shown to rob its host of 
its food. 
Mollusca. 
Indian Deep-Sea Mollusca.* — Mr. E. A. Smith has a report on the 
first set of Mollusca dredged from deep water in the Bay of Bengal. 
There are no new genera, and some of the species have a close resem- 
blance to others which occur in remote parts of the world ; two Pleuro- 
tomids have quite the appearance of northern forms or inhabitants of 
cold regions. 
y. Gastropoda. 
Cleavage and Germ-Lay er-Formation in Stylommatophora.j- — 
Dr. F. Schmidt’s embryological investigations have chiefly been made on 
Succinea putris, Limax agrestis , and species of Clausilia. With regard 
to the cleavage-process, the following are his more important conclu- 
sions. The directive corpuscle, soon after its extrusion, divides into two 
equal cells ; it remains connected by a cord of albumen with the egg 
until the latest stages of cleavage. 
The second plane of cleavage, which like the first is vertical, is at 
right angles to the first, and lies in such a way that the four spherical 
cells, which are exactly like one another, lie in the same plane. The 
next plane of cleavage is horizontal, and therefore perpendicular to the 
two first, divides each of the four cells into a larger part, and one much 
smaller, which is turned towards the animal pole. The next plane is 
likewise horizontal, and divides the four large cells at the vegetative 
pole into two unequal elements. The smaller cells at the animal pole 
are next divided into two by a vertical groove ; the next again divides 
the vegetative cells, and the whole mass now consists of twenty cells. 
The difference in size between the cells at the animal and the vegetative 
poles remains during the whole course of segmentation. On the whole, 
then, the author gives a similar history of cleavage to that detailed by 
other observers of the development of the Pulmonate Gastropods. 
With respect to the origin of the mesoderm, the following conclusion 
may be formulated ; there is so far an agreement in the formation of 
the mesoderm of Gastropods that it takes its origin from the primary 
endoderm, either early in the form of primitive mesoderm cells, or, later, 
in the form of an outgrowth from the archenteron. 
Gonads of Ancylus.J — Prof. Lacaze-Duthiers describes the repro- 
ductive organs of Ancylus fluviatilis. The hermaphrodite organ is small, 
its elongated conical acini converge to the “ androgynous canal.” 
Leaving the essential organ, this duct becomes associated with the 
albumen gland, though the author objects to this term. The sperm- 
duct and oviduct follow, and the different routes of spermatozoa and ova 
are compared to the passage of the food through the ruminant alimentary 
canal. A second annexed gland is the shell-gland. The copulatory 
* Ann. nnd Mag. Nat. Hist., xiv. (1894) pp. 157-74 (3 pis.). 
t Zool. Jahrb. (Abth. f. Anat ), vii. (1894) pp. 688-717 (1 pi., 1 fig.). 
J Comptes Rendus, cxviii. (1894) pp. 560-6. 
