770 
ROBERT PAYNE BIGELOW 
In a little older one of these specimens the rhopalium. fig. 36; 
is of the same character as in the Pelagia stage of Chrysaora 
but there is only the merest rudiment, if any trace at all, 
of the lateral ectodermal thickenings. It is rather difficult to 
compare this larva with an\ of Haeckel's genera. It is 3 mm. 
in diameter, has a simple quadrate mouth, eight gastric fila- 
ments, one in each pair being shorter than the other, and the 
tentacular pouches are a little shorter than the rhopalial ones. 
The pockets into the marginal lobes from the rhopalial gastric 
pouches are hardly large enough for a Palephyra and the pockets 
from the tentacular pouches show an approach to a Zonephyra- 
stage. The short tentacles like the buds in the younger stage 
are solid for the greater part of their length. This is the specimen 
that I spoke of in my preliminary paper as one just passing into 
the Pelagia stage. 
I have no specimens of Dactylometra in the Pelagia-stage ; all 
of my remaining larvae have acquired the rudiments of the second 
set of tentacles, and are therefore in the Chrysaora-stage. It is 
evident that, as in Chrysaora, the first trace of the dorsal sensory 
groove appears with the second set of tentacles. In a specimen 
18 mm. in diameter in which the tentacles of the second set are 
about 3 mm. long, the sensory groove may be seen as a flat disk 
of cuboidal or columnar cells lying directly above the base of the 
rhopalium, fig. 37. The sensory niche is broad and shallow and 
is lined with the ordinary flat epithelium of the body. The 
rhopalium shows all the characters of that organ in the adult 
Chrysaora; the rhopalial canal penetrates the distal part in 
the same way, the layer of nerve fibers and the supporting mem- 
brane show the same thickenings and in my sections Schewi- 
akoff's supporting cells can be seen very clearly. The rho- 
palial ridge is very short and is completely covered with the 
thick pitted epithelium, fig. 37; this is continued into the rela- 
tively very large lateral ectodermal pockets and lines of the floor 
each pocket and fills its inner half, fig. 38. The roof of the pocket 
is lined with the ordinary flat epithelium of the niche. At the 
edge of the pockets the epithelial pits are wide and compara- 
tively shallow, evidently in the process of formation; the layer 
