259 [YerriU. 



of the soft parts of Mollusca, producing little or no contraction ; and 

 for fishes and other vertebrates, and worms, etc. It also preserves many 

 plants, fruits and flowers, much better than alcohol, — the green color 

 of mosses, especially, is beautifully preserved. 



Mr. Verrill also spoke of the advantages of using a mixture of 

 transparent gelatine and glycerine, instead of Canada balsam for 

 mounting microscopic preparations of entire insects, prepared by dis- 

 solving their soft parts in caustic potash, and washing in dilute acetic 

 acid. The mixture consists of gelatine dissolved in a small amount of 

 water, with about one fom-th as much glycerine, and is to be applied 

 warm, in a manner similar to that used for balsam. The specimens 

 mounted in this way do not require drying, and may be transferred 

 directly from the water in which they are washed, to the slide. After 

 the thin glass has been pressed down, and allowed to remain a short 

 time in a cool place, the mixture becomes quite firm, and may be 

 cleaned from around the edges of the thin glass, and a circle of some 

 cement applied so as to guard against any injury from dampness. A 

 mixture of India rubber and mastic dissolved in chloroform answers ad- 

 mirably for this purpose. Upon specimens of insects prepared in this 

 way he had been able to make many interesting observations upon the 

 cellular structure of the integument, and the morphology of the 

 organs. The cells of the rings of the abdomen, both in the thickened 

 portions and the thin membrane between, in the elytra of beetles, and 

 of most other parts are brought out beautifully in these preparations. 

 One fact of considerable interest that may be readily demonstrated 

 by these preparations is, that each face of the cornea of the com- 

 pound eye is a modified cell, similar to the cells which form the integ- 

 ument of the jaws, wings, legs and abdomen, differing chiefly in being 

 more regular in form, and usually somewhat larger, though cases 

 occur in which the cells of the head and mouth parts, or the elytra of 

 beetles are as large as the facets of the eye. The form of the facets 

 is also variable, some being circular cells not very numerous and not 

 crowded, but with Intercellular spaces, as in somQ Aphidce, while in most 

 insects they become very numerous, crowded, and hexagonal or poly- 

 gonal, sometimes varying in form in different parts of the eye in the 

 same insect. In the Grape Hopper {Te't'irjonia vitis Harris), the cells 

 of the enlarged front of the head are nearly as large, and about as 

 distinct as the eye facets, and their identity of origin is perfectly evi- 

 dent. 



Mr. Verrill also gave an account of some investigations 

 ■upon the Geographical Distribution of Xorth American 

 Birds, made with reference to the physical causes that deter- 

 mine their limits in latitude. 



