SENSE-ORGANS IN MEDUSAE 
755 
THE EPHYRA STAGE IN CHRYSAORA 
The youngest specimen of Chrysaora that came under my ob- 
servation was an ephyra larva in which the tentacles were just 
beginning to bud. The eight arms of the ephyra are tipped each 
by two lobes and there is suspended from the under side, a little 
proximal to the notch between the lobes, a sense organ called 
^'Sinneskolbe" or ''Randkorper" by most German authors, the 
name rhopalium given to it by Haeckel is, however, the most con- 
venient for us and is the one I shall use. Seen from below this 
appears to be a short club-shaped structure lying horizontally 
on the under side of the umbrella, fig. 21. In describing the adult 
form the Hertwigs very aptly compare it in shape to a bent finger. 
This applies equally as well here (compare figs. 2 and 22). The 
part by which the rhopalium is attached is perpendicular to the 
oral surface of the umbrella. The other part extends at right 
angles to the first away from the mouth and in its distal end is a 
conspicuous cluster of crystals, fig. 21. The tip of the sense-organ 
reaches to the edge of the notch between the lobes. The lobe of 
the stomach that penetrates each arm has about one-third the 
width of the latter. At the base of the rhopalium it narrows into 
a small tube, fig. 22, r.c, which bends downward and extends into 
the rhopalium as far as or a little beyond the angle, where it ends 
blindly. I shall speak of this tube as the rhopalial canal. There 
is no extention of the gastric pouch into the lobes of the arm, as 
has been shown already in the figures given by Agassiz, Glaus, 
and the Hertwigs, and this seems to be generally true of this 
larval stage. 
The endodermal lamella, fig. 25, e.L, is plainly visible along the 
side of the gastric pouch, which is more or less triangular in cross 
section. The lamella extends from the lower angles of the pouch 
obliquely downward and soon joins the ectoderm and does not 
extend to the margin of the arm. 
The endoderm gradually becomes thickened towards the sense- 
organ until where the rhopalial canal bends downward the cells 
are deeper than broad. The distal end of the rhopalium is com- 
pletely filled with large thin-walled endoderm cells, each of which 
