CHOXDRIO.SOMES IN CELLS OF FISH-EMBRYOS 467 



tion be not too short ; excellent fixation of the chondriosomes was 

 obtainetl in one case (lot 38) after six days in forniol-hichromate 

 and six days in bichromate, while in another case (lot 39) simi- 

 lar results were obtained after one day in formol-bichromate 

 and eight days in bichromate. The preservation of the material 

 was not affected by leaving; the embryos in a cloudy formol- 

 bichromate solution or by changing the solution each day. 

 Although Regaud's fluid is supposed to penetrate better than 

 Benda's, a number of embryos fixed in the former showed the 

 chondriosomes well preserved in the outer layers and very poorly 

 in the chorda. The jelly surrounding, the eggs of many fishes 

 (as in the perch) proved to be an insurmountable obstacle to 

 good fixation. Poor preservation of the chondriosomes is in- 

 dicated, as I have shown ('10, 2), by the breaking of filaments into 

 granules, the swelling of granules and their transformation into 

 vesicles. 



Eggs of both kinds of perch and of Fundulus were fixed in the 

 regular Benda's mixture (1 per cent chromic acid, 15 cc; 2 per 

 cent osmic acid, 4 cc; acetic acid, 2 drops, in some cases, none 

 at all). Eggs of trout were preserved in the same mixture and 

 also in the following modifications of it: 



(1) 0.5 per cent chromic acid + 1 per cent NaCl 15 cc. 



2 per cent osmic acid 4 cc. 



Acetic acid .3 drops 



which is the formula jjroposed by Aleves ('08) for the chick-embryo. 



(2 ) Benchi two parts 



XaC'l 1 per cent aqua one part 



(3) Benda 1 , 



y , , , ,. ( equal parts 



Locke s .solution J 



(4; 0.5 per cent chromic acid + 0.5 per cent urea 15 cc. 



2 per cent osmic acid 4 cc. 



Acetic acid 3 drops 



the addition of urea l)eing suggested by a recent paper of Allen ('16). 



All these mixtures were used with approximately the same 

 results. Chondriosomes are fixed, as is well known, only in the 

 peripheral layers, but the general preserxation of the embryo is 

 excellent. The cell-limits are \'ery conspicuous. 



