ON EGGS OF MARINE ANIMALS 63 



Inclusions within the cell-membrane in a fashion which most 

 closely resembles the living state, is to be preferred to one that 

 does not. My modification of Meves meets these demands. 



Only in one respect do eggs fixed with this modified Meves 

 fall short of complete resemblance to the living: this fixative does 

 not preserve the delicate ectoplasmic structure. For this, there- 

 fore, one must use some other fixing agent. Of these, the best in 

 my judgment is Altmann's. In some cases, formalin, provided 

 it is of the best grade procurable and preferably free from formic 

 acid, is a valuable fixative. In others, corrosive sublimate may 

 be used. 



Altmann fixation 



Altmann's fixative is made up as follows: 



2 per cent osmic acid 5° ^c. 



5 per cent potassium bichromate 50 cc. 



Depending upon the egg under study, I reduce the amount of 

 osmic acid sometimes to 25 cc. Also, I frequently take 3 per 

 cent potassium bichromate. Again, I use often the formula 

 employed by Mathews (1901) in his study on the amphibian 

 pancreas, a fixation which I find most excellent. 



Washing 



Since Meves' and Altmann's solutions contain chromic acid 

 and osmic acid, objects fixed in them must be washed in water. 

 This is in accordance with the general rule that cells fixed in 

 solutions containing salts of heavy metals should be washed in 

 water, (i) Where the object is large enough, so that the danger 

 of its being lost during washing is small, it should be washed in 

 running water for 12 to 24 hours depending upon its size. (2) 

 Eggs may be washed by placing them in a large dish of 2 to 3 

 liters capacity into which tap water drips very gently. (3) Or 

 they may be placed in glass tubes covered with fine bolting silk 

 and gently inverted so that the eggs come to lie on the silk; this 

 silk-covered end of the tube is placed on an inclined trough, on to 

 which tap water is run. The difficulty of washing by either 

 method (2) or (3) 30 to 40 sets of eggs from each of 10 or more 

 experiments which would represent a season's work at the sea- 



