ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
103 
Mollusca. 
y. Gastropoda. 
Affinities of Groups of Gastropoda.* — M. E. L. Bouvicr finds that 
Actaeon solidulus is a transitional form not only between Prosobranchs and 
Opisthobranchs, but between the latter and the Pulmonata. Some argu- 
ments in favour of this view are stated, but they will probably be clearer 
when the author has an opportunity of explaining himself more fully. 
So-called Primitive Kidneys of Gastropods.f — Dr. R. v. Erlanger 
notes the absence of the so-called Urniere from Cephalopods, Amphi- 
neura, and Solenoconcha. The term includes ectodermic external, and 
mesodermic internal, primitive kidneys. The former have as yet been 
observed only in marine Prosobranchs, and consist merely of one or 
several large ectoderm cells which lie on each side of the embryo behind 
the velum. Erlanger confirms Bobretzky’s account of the enlargement 
of these cells, and the union of the vacuoles of the cells into a saccule 
containing a brown substance. In Capulus there is but one of these 
large ectoderm cells, so that Capulus leads on to Vermetus where there is 
not even one. Nor are there primitive kidneys in Heteropods, which 
are generally regarded as pelagic Prosobranchs. The internal primitive 
kidneys are either wholly mesodermic (in Opisthobranchs only), or the 
duct portion is in great part ectodermic (freshwater Prosobranchs, 
Pulmonates, and Lamellibranchs). The internal mesodermic kidney of 
Opisthobranchs is a closed sac with colourless fluid. Fol found no trace 
of these organs in Pteropods. Of their origin in Aplysia, Mazzarelli 
writes to Erlanger that they appear as two groups of mesoderm cells 
near the posterior and ventral margin of the velum, and that a closed 
cavity developes within the group. The author refers to his own 
description of the Urniere in Paludina and Bythinia ; that of Lamelli- 
branchs is more complicated ; that of freshwater Pulmonates yet more 
so. It seems to the author that the external primitive kidneys of the 
marine Prosobranchs are really homologous with those of other Gastro- 
pods and Lamellibranchs. 
Nephridial Gland of Prosobranchs.f — Dr. R. v. Erlanger finds that 
in the embryo of Cajpulus hungaricus , the nephridium is a single sac. 
Bobretzky has shown the same for Fusus , as has v. Erlanger for Triton 
nodosus and Nassa mutabilis. These facts are against Perrier’s hypo- 
thesis that the nephridial gland, such as Cajpulus and others have, 
represents a degenerate left (after torsion) nephridium. The author is 
inclined rather to regard the gland as an acquired differentiation of 
nephridial tissue or possibly as an ectodermic gland secondarily fused 
with the nephridium. At all events, Capulus shows no trace of a paired 
nephridial rudiment. 
Development of Cassidaria.§— Dr. R. v. Erlanger describes some 
abnormal phenomena in the development of Cassidaria echinophora. 
Each pea-like capsule of the large round mass of spawn contains about 
300 ova ; there is not space enough for all of these to become larvse, 
hence the abnormalities. The unfertilized ovum showed at one pole a 
* Comptes Rendus, cxvii. (1893) pp. 68-70. 
f Biol. Centralbl., xiii. (1893) pp. 7-14. 
X Zool. Anzeig., xv. (1892) pp. 465-8. § Op. cit., xvi. (1893) pp. 1-6 (3 figs.). 
