228 BULLETIN OF THE 
peculiar, but follows the laws of growth so often described in these structures 
in related genera. ; 
The cluster of medusa buds is confined to the terminal end of the lateral 
branches, Near the base of attachment of each bud there is a patch of red 
pigment. As the medusa grows in size and the proboscis begins to be formed, 
the shape of the bud gets elongated, cylindrical, and at the same time two 
opposite tentacles push out on its free margin. The proboscis has a yellow 
and orange color. The reddish patches of pigment near the base of attach- 
ment of the immature bell persist even after the medusa has detached itself 
from its connection with the lateral branches. 
The different layers of the body of the medusa bell (Plate IV. Fig. 4) can. 
be readily seen through its transparent walls. Of these the epiblast, hypo- 
blast, and intermediate layer can be easily recognized. The origin and growth 
of the radial tubes, and the subsequent formation of the circular or marginal 
canal, was traced. This growth does not differ from what has already been 
described in Syncoryne (Sarsia) and several other genera. 
The fish (Seriola) was kept alive in an aquarium for several days, and from 
the attached hydroid many free medusiform gonophores were raised. On the 
morning following the day when the fish was captured, many medusze were 
found in the aquaria, and every day after its capture many specimens ripened 
from the undeveloped buds, and one by one detached themselves from their 
union with the gonosome. There is no possibility of a doubt that the free 
medusa, as here described, has detached itself from the gonosome attached 
to the body of the fish. 
The free medusa (Plate V. Fig. 1), when it breaks its connection with the 
gonosome, has two short tentacles situated opposite each other on the bell 
margin. The medusa bell long before detachment had begun the peculiar ex- 
pansion and contraction which precede separation, and when once free moves 
gaily about in the surrounding water. Shortly after its detachment, the me- 
dusa with two tentacles resembles a young Stomatoca.* The structure of the 
Hydrichthys medusa just escaped from its attachment to the gonosome is as 
follows. 
The bell is oval, without apical projection, and recalls in outline that of 
Sarsia, The outer surface is dotted with numerous nematocysts.t Bell walls 
colorless and transparent. There are four broad radial vessels and a marginal 
tube. The tentacular bulbs are reddish, without ocellus. Two tentacles arise 
from tentacular bulbs diametrically opposite on the bell margin. No otocysts 
on the bell margin, The proboscis is cylindrical, of an orange and yellow 
color. There are patches of red pigment near its attachment, The mouth is 
simple, with entire margin destitute of appendages. 
* The fact that Stomatoca is a medusa of Perigonimus was pointed out by 
Haeckel, Allman, Hincks, and others. 
+ These nematocysts are most prominent in younger stages in the growth of 
the medusa. They are well marked even before the medusa form is attained. 
