102 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



In order to study the eggs, it is of course necessary to dissect them 

 from the mother. Tliis, again, is a tedious and delicate process, and it 

 is rarely possible to free the egg entirely from the closely applied ovi- 

 duct and ovary. This fact causes excessive trouble later, since the 

 fragments of oviduct and ovary attached to the egg prevent one's 

 placing it in any desired position or rolling it about at will, under a 

 cover-glass. 



For surface study of the early stages the eggs were then mounted in 

 glycerine under a cover-glass supported by bits of capillary tubing thick 

 enough to allow free motion to be given to the object. It was found 

 impossible to use to advantage any stain for this study, because all the 

 stains tried colored the cytoplasm more than the nucleus, and made the 

 egg so opaque that cell boundaries and nuclei could not be distinguished. 

 For the stages from one to about sixteen cells, eggs fixed in Flem- 

 ming's solution are the best, as the slight darkening produced by this 

 reagent is of advantage in stages where the egg is cleft into but few 

 cells. For later stages this darkening is a disadvantage ; eggs killed by 

 otlier methods, or bleached after fixing with Flemraing's fluid, must be 

 used. 



The eggs were moved about by rolling the cover-glass on its rollers, 

 and drawings were made of different views thus obtained. It is here 

 that the ovary and bits of oviduct attached to the egg cause infinite 

 delay and vexation, in preventing the eggs from rolling easily or rest- 

 ing in any except certain positions. The time required for the work is 

 certainly doubled, perhaps more than doubled, by this. 



With early stages, camera drawings can be made at once ffom the egg 

 after a favorable position is gained ; but after the egg has reached a 

 stage of about thirty cells, it is necessary first to roll the egg and make 

 many tentative free-hand drawings of the diff"erent surfaces, until 

 together they show the whole surface of the egg and the relation of 

 every cell to all surrounding cells. The egg is then oriented and a 

 camera figure made w^hich shows the exact form of the cells in the 

 middle region of the upper surface, and the position of all the nuclei of 

 that surface. The cell boundaries about the periphery corresponding 

 to these nuclei are then supplied from the free-hand sketches. This 

 method, while not giving mechanical accuracy for the form of the. cells 

 about the periphery of a late stage of cleavage, does permit of complete 

 accuracy so far as the relations of cells to one another are concerned ; 

 any other method with eggs in which the cell boundaries are so 

 faintly marked ou the surface is impracticable. 



