TO THE EMBRYOLOGY OF AMPHIBIA. 15 



of the ether used in dissolving it. I now tried gelatine. An egg- 

 was taken out of the forthy substance with forceps, and its orienta- 

 tion was noted. Gelatine which had previously been warmed on 

 a sand-bath was dropped from the point of a needle on the 

 mirror-surface and on its cooling, the egg was placed in the 

 desired position on the gelatine drop which was then further 

 cooled by pouring water into the mirror- dish. This gave some 

 very satisfactory results (see Egg C). But if the drop of gelatine 

 be too large or too thick in its consistence, the egg will be 

 strongly compressed and may become deformed by the swelling 

 up of the gelatine caused by absorbing water. Moreover, in the 

 later part of the breeding season when the weather gets warm, 

 the gelatine seems to become too soft to keep the egg in its place 

 and it may thus become detached. 



The method I have found most satisfactory so far, is the 

 following : — instead of fixing the egg directly on the mirror, a 

 small square piece of cover-glass, about the size of the mirror is 

 cut, and this being gently heated for about 20-25 seconds, on the 

 warm ed^e of a sand-bath which should never be hotter than 

 one's finger can bear, the egg is quickly placed on it. The 

 coagulation of the egg-envelope attaches the egg firmly on the 

 glass which is then to be fixed on the mirror by gelatine in the 

 manner described above. The least possible quantity of gelatine, 

 of very weak consistence is enough to fix a small piece of glass 

 on the mirror, the two surfaces coming into close contact with 

 each other and not detaching to the end of the experiment* A 

 very necessary precaution is that the water should be poured 

 into the mirror- dish with the greatest possible gentleness. Eggs 

 prepared in this way can be observed continuously for five or 

 more days without the least inconvenience. 



