No. 2.| DEVELOPMENT OF MANICINA AREOLATA. 195 
consecutive series of stages. When I began to section, I found 
that inferences based on the length of the larva’s life were only 
true within wide limits. 
The stage with eight mesenteries is followed in a day or two 
by the stage with twelve. At this period the first deposition of 
the skeleton makes its appearance as a circular patch of calcare- 
ous matter on the basal surface of the attached polyp. I was 
not able to rear the young corals beyond this point; though I 
kept a few alive until the first of June. The death rate increased 
very much as soon as the larvz became attached. 
III]. Earty STAGES, INCLUDING THE FORMATION OF LAYERS. 
The diameter of the unsegmented egg was about two-thirds the 
long diameter of the blastosphere (Fig. 2, Pl. II.). There was 
a very large centrally-placed nucleus, and the body of the egg 
was filled with vesicles, resembling in this respect the endoderm 
of the subsequent planula. The only observations on the seg- 
mentation were made on the eggs accidentally (?) discharged 
March 21. The spermatozoa played round each egg in large 
numbers. After fertilization the spherical egg became oval, 
and then divided into two equal blastomeres, which remained 
connected by a bridge of tissue. The division into four then 
followed. So far the segmentation was quite regular, but irreg- 
ularities now began to crowd in, which led to the production of 
a grotesquely shaped mass comparable with the irregular planula 
described by Metschnikoff for Oceania (2). (I have observed a 
precisely similar segmentation and planula in an allied medusa, 
Turritopsis.) The irregular mass did not develop any further. 
The normal segmentation which goes on in the body of the 
parent results in the formation of a blastosphere with a very 
large cavity (Fig. 1). The blastosphere is markedly bilateral, 
and is without cilia. The cells contain a large number of very 
distinct vacuoles, pretty evenly distributed through the cell 
body. In older blastospheres, Figs. 2 and 3, the formation of 
the larval or primitive endoderm has begun. The blastosphere 
cells are columnar, the nucleus is peripherally placed, and the 
vacuoles are concentrated in the central end of the cell. The 
cells are evidently delaminating, the inner vacuolated ends 
being split off to form the endoderm. The nuclei of the endo- 
