MUSEUM OF COMPARATIVE ZOOLOGY. 267 
newly forming organs in their relation to the cavity of the primitive 
hydrophyllium. 
We recognize in this stage many organs which have already been de- 
scribed, and one or two new ones lately formed. In the first place, the 
yolk —a prominent spherical mass of polygonal segmentation spheres 
with the internal protoplasmic network — should be mentioned. This oc- 
cupies most of the middle portion of the figure. Around it in profile the 
epiblastic and hypoblastic layers, of which the former is ciliated, may be 
seen. The larger, more transparent body, seen above and on either side 
of the yolk, is the projecting primitive hydrophyllium. This distal por- 
tion of this scale is represented at the top of the figure, the proximal at 
the lower part, while the right hand of the figure is the left of the scale, 
following the nomenclature of previous descriptions. The nuclei of the 
epiblast and the polygonal outlines of the epiblastic cells are easily seen 
here and there over the surface of the scale. The cavity (c.p. /.) of the 
primitive larva has two or more thread-like structures (ji/.) extending 
from its hypoblastic lining to the nuclei of epiblastic cells. The hypo- 
blast of the primitive cavity has a yellow color, especially well marked 
at its distal end, where its walls are likewise covered with small pigment 
dots, black, or nearly so, in color. At the opposite extremity of the 
primitive cavity, near the float, it ends in a closed cone-like termination, 
which is hidden by the float in the figure. 
It is perhaps needless to say, that the spherical body near the middle 
of the figure is the float, seen through the yolk contents ; and that on 
the right and left sides of the primitive cavity are two buds, which later 
develop into the serrated hydrophyllia characteristic of the Athorybia 
stage. In both of these can be recognized a very thick outer layer, 
which is probably the middle gelatinous layer, over which is spread a 
thin layer of epiblast, and an inner thinner layer, which is hypoblast. 
Within this last layer in each case we have a cavity which is the begin- 
ning of the future tube which penetrates the scales. A considerable 
quantity of reddish pigment is found in the yolk in the immediate neigh- 
borhood of the last-mentioned organs. It is very difficult for me to 
formulate any law for the relative position in which the successively 
appearing buds of the larva of the Agalma develop. We know that in 
the adult Agalma those nectocalyces which are nearest the float are the 
youngest, and that the newly formed organs of this name always develop 
between those already formed and the float. 
Fig. 2, Pl. IV. represents a very instructive stage in the development of 
the primitive larva, which was taken on August 9 at noon, or on the third 
