MUSEUM OF COMPARATIVE ZOOLOGY. 269 
larva from the side opposite that on which the primitive hydrophyllium 
is attached. The primitive cavity is thus thrown behind the yolk, and 
is concealed by the buds which have already appeared, one of which is 
shown in profile. The larva is placed in what is considered its normal 
position comparable with the natural position of the adult. The float 
is well developed, and resembles closely that of the adult. Below it 
there is a well-marked red pigment-spot on the external walls of the 
ovum, which forms a convenient point for the orientation of other organs, 
and which itself forms in later stages a well-known organ (embryonic 
tentacle) ; and at the pole of the egg opposite the float we find the 
partly formed polypite. The lower part of the large transparent body 
behind the yolk is the distal rim of the hydrophyllium ; the upper part is 
the proximal border. The axis of the future Aga/ma is thought to pass 
lengthwise through the float, and to cut also that pole of the yolk at 
which the polypite is forming. ‘ . 
The axis of the larva, as thus indicated, does not coincide with that 
which originally passes through the egg from the point at which the first 
elevation of epiblastic and hypoblastic layers took place to the opposite 
pole. It is apparently at right angles to this. If [ am right in regard 
to the relationship, or, to use a stronger word still, the coincidence, of the 
former axis with the first plane of cleavage in the unsegmented ovum, 
the axis of the adult Agalma is at right angles to the first plane of 
cleavage. It may be mentioned at this point, that in the gonophore, 
as the egg first forms, the axis of the ovum passing through the red 
pole and the point of attachment of the gonophore is normally at right 
angles to the axis of the Agalma. The horizontal diameter of the larva 
at this stage is.70mm. The vertical diameter is .75mm. The longer 
axis of the ovum is .45 mm.; the shorter, .35 mm. 
Fig. 1, Pl. IV. is taken from a larva a little older than the last, but 
still five days old. It resembles the young Agalma Sarsii at the close 
of the second week. The axis is placed vertical in the same position as 
that of the adult as usually represented. The separation of the hypo- 
blast from the yolk-cells has left a cavity of relatively considerable size 
at the point where the polypite has begun to form. This cavity recalls 
a similar cavity in the larva of Crystallodes as figured by Heckel. 
There is as yet no apparent diminution in the size of the primitive 
hydrophyllium, and the outlines of the epiblastic cells upon it can be 
easily traced. The yolk-cells still enclose the protoplasmic network, 
and have the same polygonal shape as earlier in their history. The 
float is more elongated and lies on one side of the yolk. It is filled 
