1904.] NATURAL SCIENCES OF PHILADELPHIA. 331 



above and the sperm, which is the smaller, below. The clear granular 

 protoplasm of the egg together with the sphere material surroimds both 

 nuclei. The upper surface of the egg has resumed its former rounded 

 outline, pushing the polar bodies farther outward. Their connection 

 with the egg does not appear to be a very intimate one for they do not, 

 in most cases, maintain at a later period any fixed relation to the poles 

 of the egg and so are of little value in orientation, though they are 

 often found in the apical region. 



Unsegmented Egg. 



The unsegmented egg of Fiona averages in diameter 80 micra with 

 polar axis slightly less. The two polar bodies lie at the animal pole. 

 Though the ovum is rather densely yolk-ladened, the yolk globules are 

 of such small size that in future cleavages they tend to become more 

 equally distributed among the resulting blastomeres than is the case 

 with eggs containing yolk in larger spheres. The yolk which en- 

 croaches upon the more protoplasmic environs of the nucleus consists 

 of smaller globules, but otherwise its distribution throughout seems 

 quite equal. 



The universal distribution of yolk to all the cells of the segmenting 

 egg of Fiona is probably to be correlated with the smaller size of the 

 individual yolk globules. It is safe to infer that each yolk body in an 

 egg, whether it be small or large, is surroimded by a thin layer of 

 protoplasm. In eggs containing a relatively larger number of yolk 

 globules or, in other words, where they are small in size, a greater 

 amount of cytoplasm will be distributed throughout the egg, when 

 compared with that aggregated around the nucleus, than is the case 

 when the single aggregations of yolk are large. When this is the case 

 and division occurs the whole mass will be more influenced b}^ nuclear 

 and cytoplasmic divisional activit}^ than when the cytoplasmic con- 

 stituents are more definitely separated from the yolk. Just what this 

 activity is we do not know, but a comparative study of eggs showing 

 large macromeres with those like Fiona, in which cleavage is more 

 equal, will, I think, show that in the former case the individual yolk 

 masses are much larger than in the latter, thus allowing for greater 

 cytoplasmic influence where more finely divided yolk is found. The 

 more equal division of cells naturally results in a wider spread of yolk 

 through the developing organism, and it might also be added, as a corol- 

 lary to this, that the absorption of more finel}^ divided yolk is doubtless 

 much more readily accomplished than where large globules are fomid, 

 thus rendering it possible that such a wide distribution should occur in 

 cells not alimentarv'in function. 



