THE DEVELOPMENT OF ALCYON1UM DIGITATUM. 
65 
Early Embryos in Section. 
The granular protoplasm of the unsegmented egg is full of 
yolk globules. These are largest towards the periphery, while- 
a shallow surface layer of the egg is finely granular and 
devoid of yolk. These areas are still visible in the eight and 
sixteen cell stages (PI. 3, fig. 13), the finely granular surface 
layer being confined to the outer edge of the blastomeres. 
The yolk distribution in the later morula stages has been 
already described, the large round nuclei being surrounded 
by a deeply staining finely granular area (PL 3, fig. 20). 
Other Types of Segmentation. 
One embryo was sectioned in which an irregular outer layer 
of blastomeres had been cut off from an inner undivided mass. 1 
This example agrees with lvowalevsky’s description of the 
segmentation of the egg of Alcyonium (8). In this he relates 
how a complete covering layer of nucleate ectoderm cells of 
various sizes was cut off from an undivided central yolk mass, 
which itself split later into a few large cells, while further 
divisions of all the cells resulted in a morula similar to those 
now described. Hickson (4) records a four-celled embryo, 
and during the present investigations one embryo was followed 
to the late morula stage from two unequal blastomeres. 
8. The Pre-planula. 
After the twentieth hour the spherical morula becomes very 
gradually distorted, slowly protruding blunt lobes separated 
by corresponding depressions (Text-fig. 2). It is found that 
at this time the numerous yolk globules in the columnar 
ectoderm and the polygonal endoderm are still small and 
quite similar in the two layers. About the fiftieth hour, when, 
the prominent lobes very slowly begin to soften down again, 
1 Very possibly this egg was unhealthy; it is quoted because 
Kowalevsky's account of the early development of the egg of Alcyo- 
nium differs so greatly from what is described above. 
VOL. 62, PARI’ 1. N'EW SERIES. 
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