MICHIGAN ACADEMY OF SCIENCE. 79 



envelopes are left intact, it is important to preserve the eggs in 

 fonnalin rather than in alcohol, since the latter causes the en- 

 velope to shrink and become tongh, and usually renders the egg 

 worthless. 



Although formalin is such a valuable reagent for tixing and 

 preserving frogs' eggs, it does not follow that it is good for all 

 amphibian eggs. On the eggs of Aniblystoma, formalin has a very 

 pernicious effect. 



For fixing frogs' eggs after the closure of the neural folds, I 

 have used Lavdowsky's mixture with very satisfactory results. The 

 envelopes must first be removed, but this may be done rapidly in 

 these stages. I have not tried the solution for early stages. The 

 formula is as follows : 



Formalin, Schering's 10 parts 



Alcohol, 95% 50 parts 



Glacial acetic acid 2 parts 



Water 40 parts 



The material should remain in this solution for a day or two, 

 then it should be preserved in 70% alcohol. 



EMBEDDING. 



It is helpful to leave the embryos for a day or two in a mixture 

 of 52° paraffin and xylol, at a temperature of about 40° C, before 

 putting them in pure melted paraffin at the higher temperature. 

 Infiltrate in 52° paraffin at a temperature not to exceed 55°, for 

 several hours, changing the paraffin once or twice. 



In the early gastrula stages, the embryos are difficult to orient 

 in melted paraffin, because of the faintness of the landmarks. This 

 difficulty may be reduced to a minimum by attention to the follow- 

 ing details: Use bright daylight or a strong Tungsten light. Imbed 

 in a shallow paper box resting on a black plate. The work is best 

 done in a warm room or over a warming oven. Use a hot needle 

 to keep the paraffin melted. Orient under a lens. Several eggs 

 may be oriented in one box; they should be placed close together 

 in a row, to save time in cutting. 



STAINING. 



The embryos may be stained in bulk in Grenacher's borax car- 

 mine, which should be allowed to act for a day or two in a warm 

 ]-oom. Destain in 70% alcohol containing 0,25% hydrochloric acid. 



