4 
MONICA TAYLOR. 
24. Some of these same eggs^ extracted and preserved on 
the 17th, are described as Stage 23. 
For the following descriptions, whole and sectioned eggs 
and embryos fixed in corrosive acetic and formalin were 
examined, as well as stained and cleared preparations of 
blastoderms and of whole embryos removed from the under- 
lying yolk mass. The external appearance of the embryo 
varies a little with the fixative employed, as may be seen by 
comparing PI. 1, figs. 5 and 5 a. These two eggs are of 
about the same age, but that figured in 5 a was fixed in 
corrosive acetic, that figured in 5 in formalin. 
For stages beyond 24 whole specimens stained and cleared 
in xylol were consulted as well as opaque specimens and 
sections. 
II. General Sketch of Development. 
The preserved specimens up to Stage 20 were mostly col- 
lected from three nests, and were fixed in formalin, warmed 
or cold. No eggs were found in the coelom of female 
Sy mbranchus. 
The laid egg is spherical and has a diameter of 3'4 to 3’5 
mm. Its capsule is firm and somewhat tough and separated 
from it by fluid. A mass of what looks like a coagulated 
albuminous substance is present at the vegetative pole. When 
the capsule is removed this substance separates away, so that 
the egg appears to be sometimes no longer spherical but 
somewhat oblate, the equatorial diameter being the greater. 
It is also very brittle. 
The youngest specimen in the collection is described as 
Stage 5 (PI. 1, fig. 1). At this stage the blastoderm is very 
well marked. It looks like a white circular pad let into 
the yolk-mass, this pad being composed of small white cells 
and measuring about 1 mm. in diameter. It stands above the 
surrounding yolk to a height of nearly *5 mm. The animal 
pole is flat in comparison with the distinctly spherically curved 
vegetative pole. 
