382 Transactions of the Society. 



of the nerve-cells becoming very clear. The cells of the liver and 

 green glands, and those of the hypodermis were also brought into 

 view in a manner that left little to be desired for clearness. 



By no means the least important point about these larvae is 

 that, delicate as they were, they could, after the treatment de- 

 scribed, be clarified with oil of cloves and mounted in Canada 

 balsam, with little or no shrinking or distortion. 



For Dajyhnia, I have lately found the same treatment a decided 

 success. The heart, alimentary canal, ovary, and appendages are 

 well brought out ; the nervous system not so well, owing, I suppose, 

 to its containing less fatty matter than that of Phyllosoma, and 

 consequently not being acted upon to the same extent by the acid. 

 For entire specimens an exposure of ten minutes to half an hour in 

 1 per cent., or of twelve to twenty-four hours in yV per cent, is suffi- 

 cient ; but for dissected specimens, to show the separated appendages, 

 a day in 1 per cent, is not too much, the chitin becoming stained of 

 a light brown colour by the long exposure. In one specimen 

 acted on for this time I was fortunate enough to get the heart 

 dissected out of its pericardium, and found that the organ showed 

 very perfectly the beautiful arrangement of muscular fibres figured 

 by Glaus.* It must be remembered that after twenty-four hours' 

 exposure to a 1 per cent, solution of the acid, the Daphniae appear 

 perfectly black to the naked eye. 



For Cijiyris, Cyclops, &c., the same process is equally good for 

 the preparation of specimens for dissection ; but very little is 

 shown when the animals are mounted whole. 



The acid is a great success for preparing the mouth parts and 

 other appendages of Asellus aqnaticus. The animals should be 

 placed entire in a 1 per cent, solution for about a day, and then 

 treated with alcohol of gradually increasing strength. They become 

 jet black to all appearance ; but when the appendages are dissected 

 off, clarified, and mounted in balsam, they are seen to be stained of 

 a rich brown colour, their muscles are brought out with perfect 

 clearness, and their finest setas well shown up. The same specimens 

 unstained are so transparent as to be almost invisible, and such 

 colouring matters as carmine and haematoxylin are anything but 

 successful. 



I have made very few experiments with insects, but those I have 

 are sufiicient to show how valuable this method is for the prepara- 

 tion of mouth parts, salivary glands, Malpighian tubules, &c., and 

 how it ought, for the former, entirely to replace the somewhat 

 barbarous method of treatment with potash or with turpentine. 



The only other application of osmic acid to which I have to draw 

 attention, is for the preparation of delicate vegetable structures. The 

 most important experiments I have made in this direction are on the 

 * ' Z'jitschr. f. wiss. Zool.,' xxvii. pi. 26. 



