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CHIYOMATSU ISHIKAWA. 
diameter, they pass into the vitellogen, to be charged with 
nutritive elements. Here they grow very rapidly, and their 
colour gradually becomes altered to a dark green. Nutritive 
elements or yolk-spheres grow and multiply rapidly on all 
points of the egg, but especially in a region near the peri- 
phery. The vacuolar spaces, mentioned above, also increase 
very rapidly in number and size, while the protoplasm becomes 
thus alveolar in its structure (fig. 14). The protoplasm which 
had originally filled the entire body of the ovum, has now 
become very scarce; i. e. in proportion to the size of the egg; 
and when the egg attains its Tull dimensions, it becomes a 
matter of great difficulty, even in nicely prepared sections, to 
discern the presence of protoplasm among thickly crowded 
vacuoles and yolk-spheres. 
This peculiar arrangement of protoplasm suspending the 
deutoplasmic elements in its meshes, is also stated to occur 
among Vertebrates ( 4 T 9 ). 
But how, it may be asked, do the yolk-spheres of the egg 
originate ? Do they develop in the protoplasm of the egg or 
do they arise from the investing follicular cells ? Lereboullet 
(A) regards them as originating in a special kind of cell con- 
taining the yolk substance, while Waldeyer ( 8 T 5 ) derives the 
yolk-elements from the follicular epithelium cells. Ed. van 
Beneden (A) says : “ I have believed, at first, that the nutritive 
elements of the vitellus had taken birth in the special cells of 
the vitellogen, and that these cells are absorbed by the proto- 
plasm of the egg-cell. But I have soon recognised that there 
is a considerable error, and that the germs never present the 
cellular appearance, if we observe them in the interior of the 
sexual utricle or in an indifferent fluid, such as the iodite of 
serum or a solution of albumen. At present I am certain that 
the nutritive elements of the vitellus always form themselves 
in the interior of the protoplasm of the egg-cell, as Mr. de la 
Valette St. George has recognised long ago.” In Astacus 
fluviatis, according to Professor Huxley (AJ4), “ the proto- 
plasm of the cell, as it enlarges, becomes granular and opaque, 
assuming a deep brownish-yellow colour, and is thus converted 
