1891.] Embryology. 583 
EMBRYOLOGY.! 
Development of the Scyphostoma of the Scyphomedusz. 
—Professor C. Claus has published a paper dealing with the early 
Stages of the embryo and the structure of the scyphostoma of Coty- 
lorhiza, Aurelia, and Chrysaora.? The paper is largely a detailed 
criticism of Goette’s work on the same subject, and a vindication of 
Claus’s preceding paper, especially on those points in which Goette 
differed from him. ‘The discovery of the ectodermal origin of the 
four muscle-bands of the scyphostoma would seem to be the only new 
point of value added by Goette. The others were either pointed out 
by Claus in his former paper, or else are now shown to be erréneous. 
Goette described the endoderm in Aurelia as arising from cells wan- 
dering from the blastula into the segmentation-cavity, where they 
united into a solid plug, attached at one joint to the wall of the blas- 
tula. Later a cavity arises in the middle of the mass, and this com- 
municates with the exterior by means of a blastopore. Claus denies 
this method of formation of the endoderm. Exceptionally, he says, 
wandering, isolated cells are found in the segmentation cavity of 
Aurelia, but the large mass of cells pushes in from the endoderm pole. 
The two or three cells which may arise elsewhere from the blastoderm 
take no part in the formation of the permanent endoderm, and seem 
to degenerate. In Cotylorhiza the gastrula arises by invagination. 
_ Goette’s statement that the lining of the proboscis is formed by an 
ectodermal invagination is verified, but there is not formed an cesoph- 
agus like that of the Actinians in the Scyphomeduse, as Goette 
affirmed. In contradistinction to the Hydropolyp, the Scyphopolyp 
has not only the ectodermal lining of the proboscis, but is also charac- 
terized by four evaginations from the part of the stomach-cavity, which 
0 to form the interior of the tentacles, and there alternating with the 
tænioles. The four septal muscles arise from ectodermal ingrowths 
from the peristome, differing in this from the Anthozoa. The sense- 
organs arise from the bases of the eight radial tentacles. 
Goette has denied that the polyp and jelly-fish in the Scyphomedusze 
are to be regarded as forming an alternation of generations. Claus 
Shows, however, that to deny the traditional alternation of genera- 
__ "ions in Scyphomedusz consists merely in giving a narrow — to 
! Edited by Dr. T. H. Morgan, mn Hopkins University, Paimas, Md. 
a Zool. Inst. Wien., T. IX., 
* 
