ON EGGS OF MARINE ANIMALS yj 



made up with mercury bichloride, as Lang or Gilson, or those 

 containing picric acid, as for example, Bouin's. Osmic acid 

 alone or in combination with chromic acid or potassium bichro- 

 mate is excellent for the study of the egg's contour and for 

 changes at the surface. As an aid for the study of the sectioned 

 ^gg^ in toto preparations are helpful since they serve as a rapid 

 means for determining stages which one desires to study in 

 greater detail. Obviously, in toto preparations give only gross 

 pictures. The practice by some so-called experts in cytology 

 of using in toto preparations for the investigation of such fine 

 cellular structures as asters and centrospheres is to be con- 

 demned. And certainly, where the whole eggs are subjected to 

 pressure — itself an experimental method — in order that they 

 may be studied under apochromatic oil-immersion lenses, inter- 

 pretation is even less valuable. 



The stains employed for in toto preparations are usually borax 

 carmine and Ehrlich's or Delafield's haematoxylin. These 

 bring out grosser structures very well. For the study of finer 

 cell structures, however, other dyes are to be preferred. 



Staining of the sectioned egg 



Stains employed for the sectioned egg may be classed as 

 nuclear stains, plasma stains and stains for mitochondria and 

 Golgi apparatus. What was said above with respect to fixatives 

 may be repeated here: no single stain serves perfectly to answer 

 all purposes. Nevertheless, Heidenhain's iron haematoxylin 

 stain is the nearest approach to an all-purpose stain, provided 

 the fixation is proper. 



{Nuclear stai?is) 



Of nuclear stains, haematoxylin is most commonly employed. 

 Safranin is excellent especially for phases of mitosis. Gentian 

 violet is comparable to safranin. The Flemming triple stain, 

 although often difficult to manage, gives results that repay the 

 worker for the time consumed in learning its use. The same is 

 true of Ehrlich-Biondi. Bensley's various combinations of dyes 

 and Pianese's staining methods, especially when followed by his 

 fixatives, have given me beautiful preparations. Here I empha- 

 size the methods which have proved most useful to me. These 



