IQI5.| J. Rrrcui1e: Aydroids of the Indian Museum. 553 
frequency of its occurrence this structure is of first importance in 
the propagation of the species, for every hydranth examined 
(except one) bore one and often two bulbs at varying stages of 
development. The solitary exception was a young individual 
with 5 tentacles, in which the proximal extremity ended in a 
sucker-like disc without perisarc, the equivalent of the basal disc 
or ‘‘ Fussplatte”’ of Hydra and other forms. The universal pre- 
sence of at least one basal bulb or its antecedent on these speci- 
mens can be readily understood by the fact that all the hydranths 
examined were growing upon a seaweed; and that as the basal 
bulb is the only means of attachment its presence was postulated 
by the stage of growth of the hydranths discovered. The only 
hydranths likely to be found lacking the basal bulb are indivi- 
duals belonging to the unattached, probably planktonic, stage. 
Position and General Structure of the Basal Bulb (pl. xxx, figs. 
I-3). The basal bulb is situated at the lower free end of the 
hydranth in the position generally occupied by the hydrorhiza. 
Resemblance to a hydrorhiza is further to be found in the fact 
that it seems to be the habit of the basal bulb to lie with its long 
axis parallel to the substratum and at right angles to the hy- 
dranth. Basal bulbs have been found in the youngest bydranths 
as well as in the oldest individuals examined ; in the former, the 
hydranth body springs directly from the bulb, in the latter the 
bulb terminates the stalk-like proximal prolongation of the hy- 
dranth. 
At all stages the character of the bulb is obscured by masses 
of organic debris which adhere to it in a dense coating and 
spread from it for a short distance upon the hydranth. Within 
this debris, except in the very earliest stages, lies a more or less 
globular shell of chitin, thin, delicate, and colourless at first, but 
later becoming strong, immobile and tinted. During its impres- 
sionable stages the chitin of the bulb may be moulded upon the 
particular substance whereon it lies, and this produces consider- 
able modification in the typical rounded form. The chitinous 
shell contains and protects a simple cellular sac, which in its more 
mature stages lies loosely within. This sac, the essential portion 
of the basal bulb, consists of a single layer of ectoderm and of 
endoderm. In its advanced stages it is connected with the proxi- 
mal end of the hydranth by a narrow protoplasmic neck which 
passes through a small circular opening in the chitinous shell—the 
only aperture connecting the interior of the shell with the exterior. 
Detailed Structure of Mature Basal Bulb (pl. xxxa, fig. 9). 
Well developed basal bulbs were examined in serial sections. In 
these specimens the cellular sac did not lie in contact with the 
chitinous investment ; but since the chitin showed many regular 
growth-lines and could only have been secreted by the sac, the 
hiatus may be artificial, due to shrinkage in preservation. 
No special features mark the single layers of ectoderm and 
endoderm which form the walls of the sac: the latter contains 
