IQI5.] J. Rrrcwte : Hydroids of the Indian Museum. 543 
hydranth or polyp, with a long stalk-like extension of the body in 
older examples, and a unique basal development which I shall 
call the “‘ basal bulb.’? ‘The basal bulb, which alone is protected 
by perisarc, is the organ of fixation, actual adhesion being appa- 
rently due to a loose mass of debris-laden mucus which surrounds 
the bulb and spreads out upon the substratum. No part of the 
polyp, in its simplest condition, secretes perisarc or mucus. As 
will be found more fully described in a later section (p. 553) the 
bulb represents a method of vegetative reproduction, and is a 
temporary structure. Basal bulbs have been observed, both by 
Dr. Annandale and by myself, isolated and without any attached 
polyp. In sucha case the polyp must either have disintegrated 
or have broken apart and become free. That the latter is the 
actual case is borne out by the condition of the isolated basal 
bulbs, which contain well-preserved coenosarc; and by the dis- 
covery of a polyp which has recently broken away from its base 
tol xxx, fig. 6). 
Further, at the breaking-off period the released polyp posses- 
ses no means of attachment, although in course of time the lower 
end of the body secretes both perisare and mucus, and gradually 
becomes modified into a new basal bulb. The details of these 
processes, so far as they have been traced, will be described in 
the paragraphs dealing with reproduction. The above more 
general observations, however, are sufficient to suggest that at 
certain phases the polyp is released from its old attachment, and 
that a period of freedom intervenes before a new organ of fixation 
has developed. 
STRUCTURE OF THE HYDRANTH. 
Form and Dimensions (see plate xxx, figs. I-3). 
An individual consists simply of an isolated polyp. There is 
no definite hydrocaulus, although the proximal end of the hydranth, 
especially in the more fully developed specimens, is extended into 
a Stalk-like portion. Nor is there any stolon or hydrorhiza in the 
ordinary sense of the term, the functions of such being performed 
by the basal bulb. 
In its living state, Dr. Annandale informs me, the hydroid 
is colourless. 
The form of a normal adult resembles an Indian-club. The 
head of the club is ovate with a broad median zone on which 
the tentacles are placed. On both sides of the tentacle-zone the 
hydranth tapers gradually away: distally into a large conical hypo- 
stome on the truncated summit of which a shallow depression 
marks the position of the mouth; proximally into the long almost 
parallel-sided handle of the club. The total length of a well-grown 
individual varies from 0°63 mm. to 0:98 mm., the length of the 
‘“head”’ from 0°28 mm. to 0°52 mm., and the diameter of the 
tentacle-zone (the greatest diameter of the hydranth) from 
o'I6 mm. to 0°28 mm. In the youngest examples I have seen 
there was no proximal extension of the hydranth, and the ‘‘ head’’ 
