Some Feathers polarise Light. 469 



not completely thrown off, but still adhering to the animal. 

 Of the precise mode and manner in which they disengage 

 themselves from their old shells I regret that I can give no 

 particular account : I am speaking of things which I witnessed 

 some thirty years ago, and perhaps, too, at the time of their 

 occurrence I might have been too intent on the chase to pay 

 much attention to minute points of natural history. I have 

 no opportunity of renewing my experiments, as the brook 

 (alas ! that it should have been so !) has long since been ruined 

 as a fishery, by having been converted into a straight unin- 

 teresting trench for the purpose of draining the wood through 

 which it passes. I can state, however, that the shell is cast 

 entire, not broken into pieces, nor split above ; so that the 

 crayfish (as we might expect) must crawl out from the fore 

 part beneath. How often, in the course of their lives, these 

 animals cast their shells, does not appear ; but, if my memory 

 serves me, exuviae, as well as soft-shelled crayfish, were met 

 with both of small and of full size. We must suppose, there- 

 fore, that the shells are renewed more than once. The opera- 

 tion too, of casting the shell, I should conclude, is not con- 

 fined to any one fixed period of the year, but is regulated by 

 other causes. My visits to the brook in question were made 

 in the months of July and August; at which season, as already 

 stated, some specimens were to be found which had recently 

 undergone the change, others about to undergo it; but by far 

 the greater number exhibited no signs either of recent or 

 future casting of the shell. 



Mr. Thompson, it should seem (p. 275.), maintains " the 

 existence of transformations throughout the Crustacea," similar, 

 I suppose, to those of the larvae of insects. Now here, again, 

 I cannot speak to the fact as regards crabs and lobsters ; and 

 I know that there are anomalies in nature. But the young 

 of the freshwater crayfish most unquestionably are hatched, 

 and come into the world in the same shape as the adult ones. 

 In the above-mentioned little brook, I have caught crayfish 

 with the ova apparently just hatched, and the minute young 

 not having yet, as it were, left the nest, but still adhering to 

 the under part of the parent. Doubtless, the experience of 

 other crayfish-catchers will be found, on enquiry, to confirm 

 the above facts. — W. T. Bree. Allesley Rectory, May 12. 

 1835. 



Birds. — Some Feathers polarise Light. I know not to 

 how many species this property extends, but I may mention 

 the feathers of the turkey, the " Argus bird," &c. On look- 

 ing at a candle through the lateral fibrillae of the feather of a 

 young " Argus bird," the phenomenon was striking and 



