264 BULLETIN OF THE 
clearly to be seen through the side of the hydrophyllium, and the en- 
veloping layers of the yolk are traceable over its whole surface. Within 
the segmented yolk cells appears the protoplasmic network (vt. c.) which 
dates back to the original ovum in the gonophore. The primitive hydro- 
phyllium is seen fitting over the ovum like a helmet, which, although 
fastened to it at the germinative pole, is free on the sides. Its border 
and sides cover about two thirds of the yolk which is here represented 
through the transparent lateral walls. 
The primitive hydrophyllium is transparent, slightly reddish in cer- 
tain regions, its great bulk being gelatinous. The following distinc- 
tion between the distal and proximal rim can be easily seen when in 
profile. The wall of the distal edge, which corresponds to the visor of 
the helmet of our former comparisons, is much thicker than the opposite, 
and more rounded. The proximal rim ends in a sharp angle, and its 
walls are very thin. In a figure of this stage we have the larva repre- 
sented as if we were looking at it from the left-hand side as defined 
above. Over the surface of the primitive hydrophyllium is spread a 
single layer of thin polygonal cells of the epiblast, which are seen in 
profile around the rim of the bell and on its bounding lines, even on 
the inner surface adjoining the yolk sac. Over the external surface 
the prominent nuclei of the same cells can be readily traced, dotting it 
at intervals, and in places well-defined cell-walls can be faintly seen. 
The layer from which these cells came, or the epiblast, was one of the 
first layers to form, and throughout the growth it has been gradually 
becoming relatively thinner and thinner. Although the bodies called 
nuclei of these cells are very well marked in Aga/ma elegans, 1 do not 
find them represented in the figures which have been published of other 
species of the genus Agalma, or Crystallodes. The remnant of that 
cavity, which has been called the primitive cavity, is now a tubular body 
with thickened hypoblastic walls of yellow color, and extends from the 
base of the float towards the distal portion of the hydrophyllium. 
At this stage in the development of the primitive hydrophyllium it 
was observed that from the nuclei of several of the epiblastic cells, situ- 
ated on the surface of the hydrophyllium above the fundus of the 
cavity, there were thread-like extensions, probably protoplasmic, which 
connect the surface of the larva with the hypoblast of the cavity. At 
times the surface of the hydrophyllium from which these threads arise 
is depressed as if forcibly drawn back by them. In a few instances the 
threads end blindly in the gelatinous layer at a point not more than 
half-way from the epiblast to the cavity. These threads sometimes 
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