MEDUSA. 29. 
visible signs of Medusa-buds in any of the specimens, and, if this species does 
reproduce asexually, then some buds should be present in the young stages. It is quite 
probable that only Eleutheria dichotoma in this genus has Medusa-buds. 
The number of the tentacles increases with age, and they are closely packed 
together round the margin of the umbrella. It is very likely that the number of 
tentacles present when the Medusa is liberated from its Hydroid corresponds to the 
number of radial canals, one tentacle being opposite each canal. The tentacles opposite 
the radial canals in the later stages have their ocelli further in from the margin 
(Plate III, fig. 2), indicating that they are the oldest of the series. Each tentacle is 
bifurcated or branched, and the bifurcation is visible soon after the first appearance of 
the tentacle. The upper branch comes off close to the umbrella, and, when fully 
developed, is provided with ten to twelve clusters of nematocysts arranged laterally 
in pairs, and a terminal cluster of nematocysts is also present. When the branch is 
expanded (Plate IIL, fig. 1) the clusters are far apart and form an alternating series, 
but in a contracted branch (fig. 4) their arrangement is pinnate. It is by the 
position of these clusters of nematocysts that this species can be easily distinguished 
from Eleutheria vallentini, which has two or three clusters on the upper (aboral) side, 
and occasionally one on the under side. The lower branch of the bifurcation is 
without clusters of nematocysts, and it terminates in a slight enlargement, the 
adhesive disc or sucker, which is composed of specialised ectoderm cells. The 
tentacles are hollow and the endodermally lined lumen extends along both the 
branches. The basal portion of each tentacle is covered on its under side with an 
extra thick layer of ectoderm containing nematocysts (Plate III., fig. 3), but there 
is no enlargement of the nature of a basal bulb. Both Eleutheria dichotoma and 
E. vallentini have a continuous band of nematocysts round the margin of the 
umbrella. This band is absent from E. hodgsoni, but it is represented by isolated 
patches of nematocysts on the basal portion of the tentacles. 
LEPTOMEDUS 
Famity LAODICID Ai. 
PrycHocrna, A. Agassiz, 1865. 
Generic Character.—Laodicide with four radial canals; with a central stomach 
and mouth; with the basal bulbs of the tentacles without ocelli (Browne, 1907). 
PTYCHOGENA ANTARCTICA. 
(Plate IL, figs. 6-9). 
Ptychogena antarctica, Browne, 1907, p. 474. 
In my preliminary notes on the ‘Southern Cross’ Hydrozoa I alluded to this 
Medusa under the name of Laodice. Later on, when I revised the Laodicide, it 
was placed in the genus Ptychogena, and a brief description of the species was given. 
Zz 2 
