76 CORRESPONDENCE. 
Correspondence, 
= 
Rectanecutar Prism.—Will some one kindly inform me where I can 
obtain the prism mentioned at p. 18?—W. H. C., Folkestone. 
[Of Mr. James Swift, 43, University Street, London, W. ; and probably 
any of the London opticians.—Hps. M. N.] 
Snow Crystats.—The easiest way to examine these is to take the 
microscope into the open air. If snow is falling, place it under some 
screen, or get afriend to hold an umbrella over it. In a few minutes the 
instrument will be of same temperature as the air, and snow-flakes may 
then be caught on a glass-slide, held by a clip, (so thatthe warmth of the 
hand shall be kept at a distance,) and examined one after another.—H. 
Snow CRYSTALS UNDER THE Microscopr.—An apparatus suitable for 
observations of this kind is described and figured in Sachs’ ‘‘ Text Book 
of Botany,” p. 658. Perhaps a simple method would be to place a lump 
of ice in a saucer, close under the stage, and let the snow crystal fall 
upon a glass slip, whose temperature had been reduced to 32°.—F. T. 
Mort, Leicester. 
Movuntine Ponyzoa anp Rotirers.—Some of your correspondents 
(p. 52) enquire how Freshwater Polyzoa and Rotifers can be mounted. I 
have mounted them very successfully by the following process :—Place 
the Polyzoa in a deep cell with some of the pond water; let them remain 
undisturbed till they have expanded their tentacles, then suddenly let 
fall a drop of alcohol into the cell. This kills them instantly. The cell 
is then filled up with distilled water or glycerine, and sealed in the usual 
way. Rotifers may be treated in the same manner, but the cell may be 
shallow.—Tuos. Listz, Wolverhampton. 
Earzty Sians or Sprinc.—A specimen of the Small Tortoiseshell 
Butterfly was captured in the garden of Mr. Lee, Sparkenhoe Street, in 
this town, on the 12th of February. On the same day the first Snowdrop 
opened its blossom in my own garden, Crocuses being an inch or two 
above the ground, Lilacs, Flowering Currants, and Deutzias showing 
green tips to their leaf-buds; and the Nuts (Fill-basket) putting out the 
red styles of their female blossoms. Laurustinus, Sweet Bay, and 
Magnolia have suffered slightly from the long frost, but less damage 
appears to have been done than I expected.—F. T. Morr, Leicester. 
Crrcunation 1N Empryo oF Trour.—On Saturday, February 15th, I 
received from Mr. T. Bolton, 17, Ann Street, Birmingham, atube containing 
the Embryo of the Trout in the “ Alevin stage,” accompanied by an 
admirable descriptive diagram, drawn by Mr. H. E. Forrest. This is one of 
the most beautiful and instructive objects for the microscope I have 
ever seen, and in my opinionis a far better subject for showing the 
circulation of the blood than either the web of a frog’s foot or the tail 
of a tadpole, inasmuch as without the least trouble or preparation, 
beyond placing it in a small zoophyte trough, the whole system of circu- 
lation, from the heart to the farthest capillaries and back again, can be 
observed in the most perfect manner. The pulsative motion of the blood 
in the arteries, as distinguished from that in the veins, which flows in a 
steady, unvarying stream, is made patent to the most superficial 
observer. I have no doubt most of Mr. Bolton’s subscribers derived very 
great pleasure from this interesting specimen, and, as I did, congratulated 
themselves on the result of their subscription to his microscopic agency.— 
Joun F. Goopr, Handsworth. 
Unvusvan Departure oF Brrps.—During the late hard weather the 
Fieldfares, Missel Thrushes, and Redwings quite left us, a most unusual 
circumstance. Up to the middle of December the first two were 
ost Ee 
