86 
CHARLES L. BOULENGER. 
thickened ectoderm containing an enormous number of small 
irregularly shaped cells, the majority of which are obvious 
nematoblasts and contain nematocysts in various stages of 
development, many being quite fully formed. The latter are 
similar in every respect to the nematocysts of the tentacle- 
batteries, and I see no reason for considering them as modified 
in any way. 
The nematoblasts of the fully formed stinging-cells in the 
nettle-ring are always without cnidocils, and, moreover, the 
capsules are orientated in such a way as to prevent their use 
as defensive organs. The characteristic elongated nemato- 
cysts are without any definite arrangement, and even at the 
edge of the nettle-ring none have their longer axes at right 
angles to the surface (figs. 2 and 3). 
It is obvious from the above that the nettle-ring cannot be 
a functional stinging-cell battery, and some other use must 
be discovered for it. Examination of the structure of the 
tentacles reveals its proper function. The tentacles of 
Limnocnida have been very carefully, described by 
Gfunther ( 4 ) and Browne ; the following account of their 
arrangement is quoted from the latter’s recent description 
of the B,. Niger specimens ( 3 ) : 
“The tentacles are very numerous and are very closely 
packed together round the margin of the umbrella. They 
are arranged in definite series showing a well-marked 
difference in size, which is due to growth. The four per- 
radial tentacles, opposite the radial canals, are the largest, 
and these are closely followed in size by the inter-radial and 
adradial tentacles. Then follow about five series of tentacles, 
decreasing rapidly in size. The tentacles in each series arise 
between the tentacles of the previous series, so that beginning 
with the four primary per-radial tentacles there come four 
inter-radial, eight adradial, and then sixteen, thirty-two, 
sixty-four, up to about 500 tentacles. 
“ The basal portion of the tentacles is partly embedded in 
the jelly of the umbrella. The length of the portion which is 
embedded varies according to the size and age of the tentacle. 
