G20 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [14] 



it acits ; tlierefore tlie eggs should not be allowed to remain in it more 

 than twelve hours. While eggs hardened in chromic acid never change 

 their form or become rfoft when transferred to water, those hardened in 

 alcohol, when placed in water or very dilute alcohol, lose their hardness, 

 swell up, and often suffer changes in form. 



"3. Alcoholic preparations are easily stained ; but chromic acid prepa- 

 rations are stained with such difficulty and so imperfectly that Hertwig 

 omitted it altogether. 



" There is an important difference between alcohol and chromic acid 

 in their eflect on the pigment of the egg. Chromic acid destroys the 

 pigment to some extent, and thus obliterates, or at least diminishes, the 

 contrast between pigmented and non-pigmented cell-layers. As the dis- 

 tribution of the pigment is of considerable importance in the study of 

 the germ lamellae, it is well to supplement preparations in chromic acid 

 with those in alcohol, in which the pigment remains undisturbed. 



" 4. Eggs hardened in chromic acid were embedded almost exclusively 

 in the egg-mass recommended by Oalberla. The great advantage offered 

 by this mass is that it supplies a sort of antidote to the brittleness of the 

 egg. It glues the cell-layers together, so that the thinnest sections can 

 be obtained without danger of breaking. 



"5. As the dorsal and ventral surfaces and the fore and hind ends 

 can be recognized in very early stages, it is important to know precisely 

 how the egg lies in the egg-mass in order to determine the plane of sec- 

 tion. In order to fix the egg in any given position in the embedding 

 mass, Hertwig proceeds as follows : 



" a. A small block of the hardened mass is washed in water to re- 

 move the alcohol, and in the upper surface of the block, which has been 

 freed from water by the aid of filtering paper, a small hollow is made. 

 This hollow is then wet with the freshly prepared fltiid mass. 



" h. The egg is washed in water to remove the alcohol, placed on a 

 piece of filtering paper to get rid of the water, turned on the paper by 

 a fine hair brush until it has the position desired ; the point of the brush 

 is next moistened and pressed gentlj^ on the upper surface of the egg, 

 the egg adheres to the brush and may thus be transported to the hollow 

 prepared for it in the block. 



" c. After the egg has thus been placed in position a drop of absolute 

 alcohol carefully applied will coagulate the ' fluid mass ' with which the 

 block was wet, and thus fix the egg to the block. The block is again 

 washed, and finally embedded in the egg-mass." 



MjLown experience with fish eggs, especially those of clupeoids, is that 

 a 1 per cent, solution of chromic acid gives good results. The eggs or 

 embryos should not be left in it more than twelve to twenty-four hours, 

 according to their size, when, after repeated washings in water, in which 

 they will not change even if kept iu it for three or four days, they may 

 be transferrefl to 30 per cent, alcohol, or even a weaker grade, then in 

 a day or so co 70 per cent. In a few days a granular precipitate is 



