19I5.] J. Rircure: Hydroids of the Indian Museum. 547 
with generally seven but sometimes as many as eleven examples. 
In a single node about 8 to 10 large cnidoblasts are present with 
their attendant satellites—a total of approximately 80 indivi- 
duals. Asa rule each cell contains only one complete group, but 
occasionally the cell-wall appears to become obliterated so that 
several groups come to lie within a cell’s boundaries. In median 
longitudinal section of a tentacle (pl. xxxa, fig. 8) the nematocysts 
are seen to lie at the periphery of the cell, radially inclined out- 
wards from the mid-point of its base. There are considerable 
differences in the structures of the two types of cnidoblasts. 
The larger individuals (macrocnides) (text-fig. I) consist of an 
almost spherical nematocyst, 74 to 8u long by 6, in diameter, 
surrounded by a thin and uniform covering of cytoplasm which 
pushes up the cell-wall, and is produced into a short delicate 
cnidocil. Atsome point in the proximal portion of this cytoplasm 
lies an elongated nucleus the inner profile of which conforms to 
the outline of the nematocyst. Contrary to the experience of 
Schneider (1890, p. 332) as regards Hydra fusca, the nucleus 
contains a distinct nucleolus. At the proximal end of the cnido- 
blast a delicate thread, the nerve fibre, leaves the cytoplasm, and 
passing across the vacuolar space of the cell merges with the cyto- 
plasm surrounding the nucleus that lies on the floor of the cell. 
The nucleus and its surrounding cytoplasm seem to constitute a 
ganglionic mass to which radiate the nerve filaments of many or all 
the cnidoblasts in a group. ‘The ganglion mass is in its turn con- 
nected with the layer of cytoplasm which covers the floor of the 
cell. None of the macrocnides possessed a simple broad cytoplas- 
mic peduncle such as forms an attaching structure in examples 
from several other species of Hydrozoa. 
The interior of the nematocyst is filled with a highly refractive 
fluid, which renders accurate observation of the internal struc- 
tures a matter of some difficulty. At the distal pole of the 
nematocyst is a circular area—the operculum—of consistency 
different from that of the nematocyst wall. From this area, 
whence the filament escapes on its discharge, a cylindrical tube of 
considerable diameter projects into the cyst, passing along its 
longitudinal axis almost to the proximal wall. In its upper half 
the tube contains a prominent opaque triangle pointing upwards 
and almost reaching the distal wall of the cyst, and this represents 
the single whorl of three major barbs which encircles the lower 
portion of the ejected filament. Similar smaller and less well- 
defined structures are sometimes apparent in the lower half of the 
tube. The lower section of the tube is kept in position by a series 
of exceedingly delicate gubernacula—protoplasmic strands which 
attach it to the wall of the nematocyst, and which are to be 
observed only under specially favourable conditions of staining 
and lighting. The proximal portion of the tube narrows rapidly 
and at its base is continuous with the filament which lies near 
to the wall of the cyst in an ascending spiral of some six loose 
coils. 
