EMBRYOLOGY OF CRYPTOBRANCHUS 91 



and may readily be removed with needles. Comparison with 

 eggs fixed after the removal of the envelopes shows no essential 

 difference in the results. 



The fixation of such large and heavily yolk-laden holoblastic 

 eggs presented a problem of considerable difficulty. A great 

 variety of the usual fixing fluids were tried, but none of them 

 succeeded without modification. After extensive experimenta- 

 tion, the mixture described below as Solution B was found to be 

 very satisfactory for all the yolk-laden stages, for surface study, 

 photography and for sectioning. 



The following fixing solutions were found useful for the purposes 

 indicated : 



Solution A. Formalin, 10 per cent. Useful for preserving 

 eggs in the envelopes for demonstration purposes, or for the study 

 of the envelopes, as it leaves the envelopes clear and preserves the 

 eggs in their natural color. Formalin is of some value for the 

 surface study of cleavage, as it brings out the faint cleavage fur- 

 rows of the lower hemisphere with great distinctness, and occa- 

 sionally gives remarkably good preparations for the surface study 

 of the cleavage of the upper hemisphere. In general the fixa- 

 tion of the micromeres is unsatisfactory, both for surface study 

 and for sectioning. Formalin is unsurpassed for fixing larvae 

 for museum purposes; for permanent preservation they should 

 be changed to alcohol. 



Solution B. Bichromate-acetic-formalin. The following pro- 

 portions must be quite strictly adhered to : 



Potassium bichromate 1 gram 



Glacial acetic acid 2§ cc. 



Schering's formalin, added at the time of using 5 cc. 



Water 92 cc. 



Fix about forty-eight hours in plenty of the solution, at a low 

 temperature; change the solution once or twice. 



Rinse in water and wash in 5 per cent formalin, in the dark, 

 for at least two weeks, changing the formalin as often as it becomes 

 discolored; preserve in 5 per cent formalin. Preservation in alco- 

 hol also gives good results for sectioning, but is not so good for 

 surface study nor for photography. 



