ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
167 
of those seas, they indicate bonds of relationship with the West Coast of 
Africa and the coast of Australia, rather than with the Indo-Pacific 
fauna of North-east Africa and .the Malay Archipelago. 
Mechanical Cause of Folds in Aperture of Shell of Gastro- 
poda.* — Mr. W. H. Dali has a short but interesting essay, in which he 
attempts to trace to a mechanical cause the folds which are frequently 
present on the columella and lip of the aperture of the shells of Gastro- 
poda. Reduced to its ultimate terms all we have is a twisted, shelly, 
hollow cone inside of which is a thin loose epithelial cone, the mantle, 
of which the external surface is shell-secreting. Inside the mantle is a 
more or less solid third cone consisting of the foot and other external 
parts of the body of the animal, which can be extended beyond the 
mantle-cone outwardly, as the mantle-cone can be beyond the shell-cone. 
The two outer cones constitute a loose flexible funnel within a rigid 
inflexible funnel, while the body-cone forms a solid elastic stopper inside 
of all. When the mantle-cone is withdrawn into a part of the shell-cone 
too small for the natural diameter of the contracted mantle-cone, it is 
clear that it must wrinkle longitudinally. The wrinkles will first come 
at the angles of the shell-cone and they will be most numerous between 
them and the aperture. Enough has been said to show the lines of 
Mr. Dali’s arguments. 
Connective Cells of Gastropoda.! — M. J. Chatin has come to the 
conclusion that the connective cell of the Gastropoda is not the simple 
unalterable structure which it is ordinarily supposed to be, and he 
describes a number of different stages. It should first be studied in its 
youth, when it is generally polyhedral in form and consists of homo- 
geneous protoplasm and a relatively large nucleus ; the nuclear membrane 
is difficult to demonstrate. As the cell grows the large size of the nucleus 
appears to diminish, but in some cases karyomegaly exists, as in the 
mantle of Zonites , of slugs, and of Prosobranchs, the circumcerebral 
tissue of snails, and the tissue around the otocyst in Cyclostoma. As the 
cell grows it alters in form so that it may be oval, fusiform, rounded or 
stellate. This last condition is by no means infrequent, and it may be 
seen, for example, in the nerve-centres of the snail. As the cell grows 
its internal structure may undergo secondary modifications, and a com- 
plex network may appear in it. Considering the activity of this 
element, one cannot be surprised at the formation of products in its 
interior. Of these, pigmented bodies are the most common. 
Arthropoda. 
a. Insecta. 
Greenland Insects.^ — Prof. C. H. Fernald calls attention to the very 
dark colour of the insects in a small collection from Greenland. He 
explains the fact by their resting on lichen-covered rocks, where the 
lichens are dark-brown or black. Natural selection would lead to the 
establishment of a dark race through the elimination of light-coloured 
individuals. 
* Amer. Nat., xxviii. (1894) pp. 904-14 (3 figs.). 
f Comptes Rendus, cxix. (1894) pp. 922-4. 
% Ent. News. v. p. 132. See Amer. Nat., xxviii. (1894) p< 964. 
