172 DEVELOPMENT OF THE FROG'S EGG 



to 58 degrees C. The egg must then be cut at a temperature 

 of seventy-five to eighty degrees Fahrenheit (24 to 26 degrees 

 C.); one often succeeds best if the microtome is placed in the 

 sunlight during the cutting. 



The segmentation-stages do not need to be stained. The 

 older embryos stain well in toto in borax carmine or in 

 hsematoxylin on the slide. Fresh material cuts and stains 

 better than that long preserved. 



Formalin preserves eggs and jelly most admirably for dem- 

 onstration. The segmentation-stages show particularly well 

 when preserved (permanently) in this solution. 



