BROOKS AND RITTENHOUSE: ON TURRITOPSIS. 445 
tides when in the open ocean. Several times the experiment of dividing 
the egg during the comparatively early cleavages was tried and the 
parts were found to continue their development without any hindrance. 
These experiments will be described more in detail later. 
Another point in which the segmenting egg of Turritopsis differs 
from that of Oceania armata is that it does not form a true cleavage 
cavity. The blastomeres always form a more or less solid embryo, 
as shown in the sections of these stages. Occasionally there are small 
spaces left between the cells ; but a true segmentation cavity that later 
forms a blastocoele is never formed. In this respect also it is similar 
to the development of Pennaria tiarella as described by Hargitt. As 
the completion of segmentation approaches, these irregular masses 
of cells gradually take on a more symmetrical form and, finally, there 
is formed an oval embryo composed of a solid mass of cells constituting 
a morula. 
The first cleavage takes place about twenty to thirty minutes after 
the polar bodies have been given off. It begins at the upper pole of 
the egg and passes down to the lower pole. Thus the egg is divided 
meridionally into two cells of approximately equal size. When 
division is complete the blastomeres do not remain in close union, but 
move apart so that the two spheres are connected by only small arcs 
of their circumference. The protoplasmic bridge, which frequently 
occurs in hydroid eggs at the lower pole just previous to the completion 
of the two-celled stage, is usually to be seen in the egg of this species; 
but it is much less conspicuous than is the case in Stomotoca. When 
it occurs, it is less definite and clearlv defined than in Hvdractinia, as 
described and figured by Bunting. Metschnikoff, also, figures a very 
beautiful example of this protoplasmic connection in the egg of Nausi- 
tlioe marginata. In Turritopsis the condition is much like that of 
Rathkea fasciculata, as shown by the last-mentioned observer, in which 
the connections instead of becoming a very definite bridge remain for 
a time as a less clearly outlined portion of the ectosarcal material. 
Protoplasmic currents may be seen at times in these connecting fila¬ 
ments. Their function does not seem to be clearly known; but it 
very probably is connected with a readjustment of the cytoplasm 
and the establishment of an equilibrium between the different blasto¬ 
meres. 
Hargitt in his paper on “The early development of Pennaria tiarella ” 
discusses the occurrence of papillae, threads, and bridges; and reviews 
