The Germinal Spot in Echinoderm Eggs. 5 
and appear as yolk-spherules scattered in a granulo-reticular matrix. The 
nuclear reticulum has become coarser but is still pale-staining. Here and 
there are scattered chromatin threads of beaded appearance. The nucleolus 
is breaking up into many intensely chromatic globular bodies. 
Successively later stages show a continuation of the above process. 
Figure 3 illustrates a stage where the nucleolar fragmentation and dispersal 
has progressed a little farther. The nuclear reticulum is similar to its 
appearance in the last stage, except that there are fewer of the beaded 
chromatin threads and, in this particular example, contraction of the nuclear 
reticulum again produced a peripheral artifact. Examples could have been 
selected where such contraction artifacts were lacking, but this particular 
one was chosen to demonstrate by comparison with figures 2 and 4 that the 
physical effects of the preserving fluid did not essentially modify the pro- 
gressive changes in the nucleolar history. The cytoplasm now has the 
appearance of mixed granular and alveolar type. The large yolk-spherules 
have disappeared, probably by a transformation into fluid, a continuation 
Fic. 1—Young ovum of Echinaster crassispina; nucleolus large, compact, homogeneous, 
intensely chromatic and with sharp contour; nuclear reticulum pale and shrunken 
away from wall at left; cytoplasm dark and coarsely granular. 1500. 
Fic. 2.—Nucleus at slightly later stage. Nucleolus breaking up into globular masses. 
Nuclear reticulum pale, but through it are scattered chromatic beaded threads. A 
portion of cytoplasm shown at left. It is still dark and granular, but many of the 
granules (yolk) have greatly enlarged. X 1500. 
of which process for all the yolk-granules, large and small, culminates in the 
beautiful alveolar cytoplasm of the ripe egg (fig. 7). Figure 4 gives a 
stage in the dispersal of the nucleolar fragments. The products vary be- 
tween wide limits, both in size and form, but most may be described either 
as globes, dumb-bells, or tetrads. 
The culmination of the process of dispersal is illustrated in figure 5. 
Figure 6 shows similar nucleolar fragments from a portion of a single 
nucleus. Most of these have the form of typical tetrads. The unit of 
structure here seems to be a globe and the individual mass a four-lobed 
