11 G BULLETIN OF THE 



various staining fluids tried, Erlich's acid haimatoxylin 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. 



TIkj result of segmentation is a one-layered blastosphere, as in 

 A. aurita. Although the diameter of the Mastocoel, 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 surftice 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. 

 auiita as described by Glaus (*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 coelenteron. At the 

 beginning of the process, and throughout its duration, the coelenteron 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 coelenteron 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 

 Nachriicken der die Mundspalte begrenzenden Zellen in das Innere des 



