455 



to some clearing agent. I always over-stained the material and then 

 decolorized in acid alcohol. For the study of the entire embryo a 

 rather faint stain is much the better; but for embryos that are to 

 be sectioned, a heavier stain is desirable. 



For clearing I used xylol, cedar oil, and clove oil. The two 

 latter I found cleared a little better than xylol, and were more de- 

 sirable also because of the fact that they do not evaporate so rapidly. 

 I kept the embryos in the clearing agent in a watch crystal; but for 

 drawing and for the study of any particular embryo, I removed it 

 to a microscope slide upon which I had built up a ring of cerasine 

 to such a height that the depth of the cell formed was just a little 

 greater than the thickness of the embryo. Then by moving the 

 cover-glass the embryo could be made to assume any desired posi- 

 tion. An embryo can be kept in such a cell for weeks at a time. For 

 the study of certain structures I found it very desirable to cut the 

 embryo in two and to remove all the enclosed yolk. The spiracular 

 openings, for instance, I could not make out until I had resorted to 

 this method. 



For sectioning the earlier stages I did not remove the egg mem- 

 branes. I found that by piercing the chorion and allowing the egg 

 to remain in melted paraffine for from eight to twelve hours it sec- 

 tioned very well. These eggs were all stained in toto in Ehrlich's 

 h^ematoxylin and then counterstained on the slide with orange G, 

 by the use of a saturated solution in 95% alcohol. I found that by 

 using this method I did not over-stain with the hasmatoxylin ; that 

 I got a much better stain than by staining on the slide; avoided 

 the necessity of running the slidesi through the different grades 

 of alcohol, and hence much danger of losing sections by washing 

 them off; and saved a great deal of time. The orange G differen- 

 tiated the yolk from, the superficial layer of protoplasm or from the 

 germ layers. The sections were cut with a Minot's rotary microtome 

 and mounted with Meyer's albumen fixative. The drawings were 

 made in outline with an Abbe camera lucida. 



THE EGG 



The egg of C fcrnigincus may be described as somewhat Para- 

 moecium-shaped, with a blunt, narrow anterior end, and with its great- 

 est transverse diameter about one third the distance forward from 

 the posterior end. The length of the egg is about 1.4 mm. and the 

 transverse diameter is about .5 mm. When the egg is laid the pos- 

 terior end makes its appearance first. 



