MUSEUM OF COMPARATIVE ZOOLOGY. 265 
have a close resemblance to certain similarly placed threads in worm 
larvee, as in the well-known Jornaria, where they extend from the cavity 
of the larva to an apical cluster of modified epiblastic cells through an 
intermediate gelatinous layer. I was unable to observe these threads 
closely enough to detect any tubular structure in them. Later in the 
growth of the larva there are two filiform bodies connecting the cavity 
of a hydrophyllium with its surface, which may possibly be the same as 
the thread-like extensions of which we have already spoken. In the 
development of Agalma Sarsit as figured by Metschnikoff, we have no 
representative of these threads in the primitive larva, or in stages of 
later growth. Heckel figures certain structures in the hydrophyllium 
of Physophora which have been found by me in Agalma, which in Phy- 
sophora have the form. of small tubes extending from the cavity to the 
surface. These call to mind the protoplasmic bodies in the primitive 
hydrophyllium of Agalma, although they are different in many respects. 
Heckel gives them a morphological significance in Physophora, and 
regards them as comparable with certain parts of the chymiferous ra- 
dial tube system of hydroid gonophores. He does not represent them 
in the younger forms, at least, of the primitive larva of Crystallodes. 
Cilia were not observed on the outer surface of the primitive covering- 
scale, but were seen on the epiblast covering the yolk at this age. 
Of the remaining structures found in the primitive larva the most im- 
portant in the future history is a spherical organ (pz. cy.) adjacent to the 
end of the primitive cavity. This body is the future float, and at this 
stage lies inside the egg, or between the yolk cells and the superficial 
covering, although no marked external elevation could be seen. The 
float is enclosed by a layer of cells which was traced continuously into 
the hypoblast of the primitive cavity, and also into the hypoblast 
which covers the yolk sac. Within the hypoblast the contents of the 
float and the hypoblastic layer were slightly separated. A continuation 
of the same layer, epiblast, reflexed from the inner surface of the cover- 
ing-scale, extends over the float and is continued over the surface of 
the egg. 
A second appendage, which assumed the form of a slight projection 
from the surface of the yolk on the left-hand side of the cavity of the 
primitive hydrophyllium, is also present in this stage of the primitive 
larva. In profile this structure (ser. hyph.) is arch-shaped, and has 
a slightly reddish color. It is the beginning of a covering-scale which, 
although provisional in nature, has given the name of “ Athorybia 
stage” to a larval condition of Agalma which follows the first or primi- 
