BULLETIN OF THE 
An older larva with circumoral ciliated band, and prominent anterior 
lobe. The prominences on the sides are lateral arms. 
An older larva, in which the calcareous rods, sp, are found in the body. 
Thirty-six hours old. 
Still older larva, one side outlined, in which the length of the calcareous 
rods has greatly increased. Three days old. 
An older pluteus from the dorsal side. 
The same from ventral side. 
Dorsal view of the oldest pluteus of Ophiopholis which was studied. 
Mouth, or, seen through the oral lobe. 
PLATE II. 
All figures drawn to a scale with camera lucida. Obj. B. B. Eye-piece 2, Zeiss. 
Reduced one half in photography. 
Fig. 
“ 
1. 
2. 
16. 
ive 
Ovum of Echinarachnius parma in its capsule. 
Same ovum with the primitive constriction, p, which forms the first plane 
of cleavage. The external pigmented layer of the capsule is not 
represented. 
Ovum in 2-cell stage. 
Ovum in which the second plane of cleavage has begun to divide each of 
the two cells of the 2-cell stage. 
A stage somewhat older. 
Outline of the four cells of the 4-cell stage, showing the two planes of 
cleavage at right angles to each other. 
Ovum in 4-cell stage. 
Ovum in which constrictions have begun to form new planes of cleavage, 
which later divide the four cells of the 4-cell stage to form the 8-cell 
stage. 
Ovum in the 8-cell stage. 
The same seen in a plane at right angles to the last. 
Ovum in 8-cell stage showing the segmentation cavity, cav. 
Segmented ovum of a stage with more cells than the 32-cell stage. ‘Two 
of the cells are represented with nuclei. 
The same, older, with segment spheres more angular and segmentation 
cavity shown. 
Blastosphere, “‘planula stage.” The cells have taken the form of a 
hollow sphere. The larva has left the egg-capsule. 
The same showing the flattening at one pole preparatory to an invagina- 
tion. (Optical section, in which the cells are not shown in the hemi- 
sphere turned to the observer.) 
Young gastrula with partially infolded blastoderm, forming the stomach, 
ga. 
Older gastrula. Outlines of blastodermic cells not represented. 
