CHROMATIN DEVELOPMENT AND HEREDITY 229 



Most of the observations recorded here were made on material 

 fixed with the fluid of Bouin. This gave splendid results when 

 used for the smaller pelagic eggs of Ctenolabrus and Stenotomus. 

 In the larger eggs of Fundulus and Menidia the structural de- 

 tails of the cytoplasm and the archoplasmic fibers are coarser 

 and the spindles are smaller. This, I think, accounts largely 

 for the fact that the chromosomal images during the anaphase 

 are somewhat less clear than in the smaller eggs. 



The large eggs of Fundulus and Menidia are easily dissected 

 from the chorion and can either be imbedded and sectioned 

 separately in the manner described by Moenkhaus, or the blasto- 

 derms can be removed from the yolk and numbers of them im- 

 bedded together. The latter method, while demanding larger 

 quantities of material, is convenient in that one obtains sections 

 in many different planes in less time than by the other method. 

 This is an especially good way to handle the smaller pelagic 

 eggs. The task of removing the egg from the membrane is 

 somewhat more tedious in this case, but if executed under a 

 binocular is not difficult. It is well to remove as much as possible 

 of the yolk from the blastoderms, for, although it imbeds and 

 sections well, during the process of staining bits of it are easily 

 dislodged and scattered over the surface of the sections where 

 they may prove bothersome. In the early stages, just after 

 fertilization , the germ disc is not formed, and such eggs must be 

 imbedded whole after removing the chorion. 



Sections were cut five or six microns in thickness and stained 

 with Heidenhain's iron-haematoxylin. Bordeaux red was used 

 in some earlier preparations as a counterstain, but, as it seemed 

 to have no particular advantage, its use was discontinued. 



Such experimental data as is thought necessary will accompany 

 the cytological observations on the corresponding material and 

 each cross will be described separately. The conclusions drawn 

 from the separate crosses will be reserved for the general discus- 

 sion of the results. 



