GLAISHER, ON SNOW CRYSTALS. 179 



This remarkable body when completely evolved (fig. 18/.) 

 consists of two portions — a rigid spiculum-like portion acutely 

 pointed at one end, and continuous at the opposite end with 

 the second portion, which is in the form of an excessively fine 

 filiform appendage less than half the length of the spiculum : 

 this second portion is generally seen to be bent at an angle on 

 the first, and is frequently more or less curved at the free end. 

 The form of the evolved trichocysts is best observed in such 

 as have floated away towards the margin of the drop of water, 

 and are there left dry by the evaporated fluid. In many of 

 them the filiform appendage was not visible, and they then 

 merely presented the appearance of a simple, long fusiform 

 spiculum. (Fig. 18 A:.) 



The resemblance of the organs now described to the well- 

 known thread-cells of the Polypes, and of certain other lower 

 members of the animal kingdom, is obvious. That they are 

 entirely homologous, however, with these bodies we can 

 scarcely yet assert. Their origin, at least, appears to be 

 different ; for if we admit the unicellular structure of the 

 Infusoria, we have the trichocysts apparently developed in the 

 substance of the cell-wall, instead of being produced in 

 special cells, as we know to be the case with the thread-cells 

 of the Polypes. 



Snow Crystals in 1855. By J. Glaisher, Esq., F.R.S. 



(Read before the Greenwicb Natural History Society.) 



The many snow crystals which fell during the late severe 

 weather, atti-acted such general attention, that I ventured to 

 announce a paper on the subject for the present evening. 

 Never do I recollect such an infinity of crystals as have lately 

 fallen beneath my observation. Generally speaking, they fall 

 at rare intervals and very sparingly, in cold and calm weather, 

 and frequently at the commencement of a thaw. In the 

 present year they have fallen under all circumstances of wind 

 or calm, with snow, and alone, during the continuance of the 

 late severe weather when the temperature varied from a few 

 degrees above zero to the freezing point, and up to the precise 

 moment of the thaw, with a temperature of from 34^ to 37°. The 

 size of these beautiful objects was by no means unappreciable, 

 and might be said to vary from 0' 05-inch to 4-lOths of an 

 inch in diameter. Their forms were so varied, that it seemed 

 scarcely possible for continuous observations to exhaust them 

 all. I therefore endeavoured to secure observations of those 

 which might be considered types of their class, trusting to a 



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