756 
ROBERT PAYNE BIGELOW 
secretes a concretion in its interior, fig. 22. These concretions are 
soluble in weak acids and vary in size and shape, but are generally 
prisms not more than twice as broad as long with conical ends and 
they seem to contain a core of organic matter. There is no sharp 
line of distinction between the cells which produce these bodies 
and the other endoderm cells of the rhopalium, and for Von 
Lendenfeld to call this cluster of cells the visceral mesoderm" is 
rather stretching analogies. 
The general ectoderm of the body is composed of very much 
flattened cells a little thickened in the position of the nucleus. In 
spots over the surface, the cells are much thicker so that they 
appear square in vertical section. These are the young batteries 
of nettle cells, figs. 22 and 26, h. At the base of the rhopalium 
the ectoderm is abruptly very much thickened and forms a deep 
covering to all but the most distal part of it, fig. 22. In this 
thickened part the cell walls are hardly to be distinguished ; the 
nuclei are thickly crowded in two or more irregular rows and 
between this layer of cells and the thin supporting membrane there 
appears a thin layer of nerve fibers. This thick ectoderm thins 
out at the distal extremity of the rhopalium until in my prepara- 
tions it cannot be recognized, but it is undoubtedly there as a very 
thin membrane. The thin supporting membrane which every- 
where separates the ectoderm from the endoderm is a continua- 
tion of the general mesogloea, which is structureless except for a 
few fibers running through it. The sense-organ of Chrysaora at 
this stage then, is quite simple; there is no trace of an olfactory 
groove, and there are no other organs accessory to the rhopalium. 
THE PELAGIA STAGE IN CHRYSAORA 
After the ephyra the next youngest stage of Chrysaora that I 
have studied is a larva six millimeters in' diameter. The begin- 
nings of the gonadia have not yet appeared, but the animal has 
eight tentacles, hollow at least for along distance. The pendant 
oesophagus is rather short, but there are four oral lobes which 
when spread out extend more than halfway to the edge of the 
disk, and there are two endodermal pockets into each of the mar- 
