368 CHARLES L. BOULENGER. 
it seems therefore probable that the female medusz are 
liberated later in the year than the males. 
The structure of the testis is quite typical, and in it the 
three tissue-zones described by the Hertwigs (7) are well 
developed. For a detailed description I must refer to the 
writings of these authors and to the paper by Giinther (8) 
on Limnocodium, where avery clear account of the histology 
of the male organs is given. 
As mentioned above, the tentacles, four in number in a 
normal individual, are given off from the umbrella edge at 
the terminations of the radial canals. 
These tentacles are very slender and of great length when 
fully extended, the latter being equal to more than twice the 
umbrella. 
At their bases the tentacles are swollen to form very con- 
spicuous ocellar bulbs, each of which bears on its ex-umbrellar 
surface, a bright red ocellus. Hach ocellus consists merely 
of a cup-shaped mass of pigmented sense-cells surrounding a 
number of clearer cells flush with the external surface of the 
bulb. 
The tentacles are hollow, their cavities being continuous 
with that of the circular canal. The ectoderm forms wart-like 
thickenings arranged in transverse rings which become very 
conspicuous and almost bead-shaped when the tentacles are | 
fully elongated (fig. 4). 
All four kinds of nematocysts described as occurring in the 
hydroid were found also in different parts of the medusa. ‘lhe 
barbed kinds are to be found scattered in the ectoderm of the 
whole of the manubrium, ocellar bulbs, and tentacles. In the 
manubrium they are especially numerous in the ectoderm 
around the mouth-opening, but they occur also in the more 
proximal parts, and are occasionally developed on the per- 
radial gonadial pouches. 
Sections of the manubrium revealed quite a large number 
of these nematocysts in the endoderm of the whole of that 
organ, situated always in the basal parts of the individual 
cells. 
