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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
spond to the endoderm sac of the crayhsh. In the latter the peculiar cell fragments 
also occur. 
If one now examines very thin sections under high powers, he finds that tbe 
granules and the granulated bodies correspond in general to the structures found in 
Alpheus. The chromatin grains appear sometimes as naked masses in the yolk, and 
stain either very intensely or faintly. They are often vesiculated — that is, they appear 
as hollow shells (fig. 241). Under favorable conditions it is easy to demonstrate the 
fact that these bodies surround particles of yolk, and occasionally they have a cres- 
centic shape, when they seem to be enwrapping a yolk spherule (fig. 240, plate 52) 
(94, p. 427). I have shown that the “secondary mesoderm cells” described in the 
crayfish by Reichenbach (163) are undoubtedly products of degeneration which are 
afterwards absorbed in the yolk. In this species the eudodermic cells which are 
loaded with yolk probably divide by multiple karyokinesis, producing nuclear nests or 
clusters, some of which in time undergo degeneration. The naked balls of chromatin 
which are found in these cells are probably formed in situ, though they unquestion- 
ably shift their position in the egg. 
In a species of Cambarus, which I studied at a stage when five pairs of appendages 
were present, the endodermal nucleus was surrounded by a thin layer of protoplasm, 
which worked its way amid the yolk so as to practically surround a pyramidal mass. 
This strongly recalls the serpentine manner in which the cells creep through the yolk 
in the egg of the lobster. 
Later, when nine pairs of appendages are represented, the endodermal cells have 
nearly reached the ectoderm. The yolk within the confines of the ectoderm has an 
irregular, pyramidal, or radial cleavage. Centrally it blends with a serum-like fluid, 
in which occasional granules or balls of chromatin are suspended. Small spherical 
bodies containing a single chromatin ball, or several balls, occur not only in the yolk 
underneath the ectoderm and in the vicinity of the endodermal nuclei, but also in the 
central yollc of the endoderm sac at various levels below the endodermal nuclei. This is 
a point of some interest in connection with the fate of these bodies. They wander not 
only peripherally but centrally. 1 Rarely we meet one which is three or four times the 
average size, having a small chromatin spherule in its center. These latter become 
absorbed and gradually disappear (94, p. 428). 
As I have already shown, the plasmic vesicles described by Bumpus (30) in the 
ovarian egg are mesodermic cells in the process of degeneration. (For the origin and 
history of these bodies see p. 152.) 
Later, according to Bumpus, the plasmic vacuoles are represented by chromatin 
granules scattered about in the peripheral parts of the yolk. 
In the early cleavage stages Bumpus says that the plasma cells are still represented 
by chromatin grains, which “are no longer confined to the periphery, however, but 
have advanced toward the center and formed an indefinite ring” (30). In the speci- 
mens of eggs in the early cleavage stages which I have studied — stained chiefly in 
Kleinenberg’s hmmatoxylon solution — 1 have never been able to detect any degenera- 
tive products whatever. They appear to have been completely absorbed or converted 
into yolk before this time. 
In a still later period, when the u -shaped embryonic area is differentiated, “the 
plasma vacuoles,” according to Bumpus, “are represented by chromatin uebuke, which 
1 The movement of these bodies is probably due wholly to extraneous mechanical causes 
