116 BULLETIN OF THE 
various staining fluids tried, Erlich’s acid haematoxylin gave decidedly 
the best results for sections. For examination of the whole embryos, 
Grenacher’s alcoholic borax-carmine and Czokor’s alum-cochineal each 
gave good results. The latter stain possesses the peculiarity of stain- 
ing embryos of different ages with corresponding degrees of intensity, 
the youngest stages being stained the least, the degree of intensity in- 
creasing with the age of the embryo up to the planula stage. 
The result of segmentation is a one-layered blastosphere, as in 
A. aurita. Although the diameter of the blastocel, or segmentation 
cavity, presents some individual variations at a given stage of develop- 
ment, it in general corresponds very nearly with that of A. aurita, as 
described by Goette (’87, p. 3). It increases slightly as the process of 
gastrulation advances. The cells of the blastosphere are usually some- 
what shorter at one pole than elsewhere, and it is from this region that 
the entoderm is formed. The nuclei of all the cells are situated very 
near the outer surface of the blastosphere. Small spheroidal bodies con- 
stitute the greater portion of each cell; they are very evenly distributed 
through its substance, except in the vicinity of the nucleus, where they 
are somewhat less abundant. Vacuoles of variable sizes are usually 
found in some of the cells. The nuclear region stains a little more 
deeply than the remaining portion. 
The method of gastrulation in A. flavidula is similar to that in A. 
aurita as described by Claus (’83, pp. 2 and 3), although it resembles 
even more closely a typical invagination. When the process of cleavage 
has resulted in the formation of a blastosphere composed of somewhat 
more than four hundred cells, a depression of limited extent appears in 
the portion of the wall which is composed of the shorter cells, From this 
depressed region is formed the entoderm, which develops as a single con- 
tinuous layer of cells surrounding a small cavity, the coslenteron. At the 
beginning of the process, and throughout its duration, the colenteron is 
in communication with the exterior by means of a narrow passage, the 
blastopore, or blastoporic canal. See also Explanation of Figures (Plate 
I. Figs. 1-4). From these figures it is apparent that only a small por- 
tion of the wall of the blastosphere is concerned in the invagination, 
and to that extent it must be regarded as deviating from the typical 
invagination, where one half of the ‘wall of the blastosphere is infolded 
to form the entoderm. The colenteron is, however, at all stages of gas- 
trulation, an open sac-like cavity, and therefore noticeably different from 
that of A. aurita, of which Claus (83, p. 3), says: “Mit dem weiteren 
Nachrücken der die Mundspalte begrenzenden Zellen in das Innere des 
