No. 1.] YOLK-NUCLEUS AND POLAR RINGS. | 
The study of eggs killed in any fixative containing osmic 
acid inclines me to believe that this lack of transparency is 
due, at least in part, to material absorbed from the body-cavity 
of the worm, and later from the albuminous contents of the 
cocoon ; for all these eggs contain in greater or less degree the 
black spots (Deztoplasm) represented in Fig. 14, which can be 
dissolved out with warm xylol or ether, their fatty nature 
thus being proved. These, however, are not the only factors ; 
for the degree of transparency shown by the young ovarian 
egg is not restored by dissolving away the Deutoplasm. 
The distribution of the archoplasm in all these eggs is 
modified by the fixative; corrosive sublimate or corrosive 
acetic are especially favorable for its study, as they cause it 
to aggregate into masses, thus producing the sharpest contrast 
between the red and the blue. In chromo-acetic preparations, 
on the contrary, the distribution of the archoplasm is much 
more nearly equal throughout the cytoplasm; but wth all 
fixatives it 1s aggregated at the centres of activity of the cell. 
I am inclined to think chromo-acetic the most reliable 
fixative, for the following reasons: 
First, it so fixes the eggs that the subsequent treatment 
with alcohols produces scarcely perceptible shrinkage; as a 
rule, eggs measured before killing and after mounting give 
almost the same diameter. 
Second, after chromo-acetic all the structures of the cell 
may be constantly and sharply defined :—the cytoplasmic 
network; the attraction-sphere, with its centrosome, archo- 
plasm, and rays; the spindle fibres; the chromosomes; the 
fertilization cone; the sperm, and the sperm granules. 
Structures that are distorted or obliterated by many other 
fixatives may be constantly and distinctly defined with 
chromo-acetic. 
I am inclined to believe that the apparently granular structure 
of the archoplasm is largely, if not wholly, due to the fixatives ; 
certainly the degree of granulation varies with the different 
fixatives, and at the points of greatest activity of the cell the 
fusing of the red and blue substances into a structureless 
homogeneous mass suggests that (at least in some stages) both 
