I9I5.] J. Rircute : Hydroids of the Indian Museum. 555 
Origin and Development of the Basai Bulb (see pl. xxx, fig. 6). 
The basal bulb is a modified portion of the hydranth body. This 
is clearly shown by a hydranth which has recently broken away 
from a former basal bulb, and is in process of forming a new one. 
The history of this specimen (fig. 6) may be taken as indicating 
the general development of a basal bulb, and appears to have been 
as follows. 
The hydranth tapers away at its basal end almost to a 
point, and here the tissues are ruptured. This narrow portion 
is the neck of a former basal bulb, and the damaged tissues show 
where the narrow neck, already prepared by increasing constriction 
and by the disappearance of the ectoderm layer, has broken 
asunder, allowing the hydranth to escape from its former anchor- 
age. The final rupture of the neck is no doubt due to mechanical 
strain brought about by the swaying of the hydranth in the water 
currents. 
So far as one can judge the free stage of the hydranth must be 
of very limited duration, for even before the traces of rupture at 
the neck of the old basal bulb have disappeared, a new basal bulb 
is in process of formation. 
Four modifications mark the development of a basal bulb. 
Its origin is first indicated by a slight constriction in the lower 
portion of the body of the hydranth. This constriction affects all 
the cell-layers: the endoderm and mesogloea are simply indented, 
but even at the early stage figured, there is already a disrup- 
tion in the ectoderm, which, although not yet severed, is reduced 
to very thin dimensions at the level of the future neck. A second 
characteristic regards the differentiation of the ectoderm of the 
basal bulb. Distal to the constriction, that is on the unaltered 
hydranth, the ectoderm is of the normal ridged type with rather 
elongated cells, but proximal to the constriction the cells are 
smaller, more regular and flattened. In the third place, copious 
masses of mucus in which debris becomes entangled begin at once 
to be secreted by the ectoderm of the basal bulb; and lastly 
the formation of mucus is succeeded by the secretion of a chiti- 
nous investment, the perisarc, which at the stage figured had only 
begun to form in the lower regions. ‘The folding over of the bulb 
until its long axis lies at right angles to that of the hydranth must 
be a subsequent development. 
While the above mode of development of the basal bulb 
happens to have come to my notice and is, on account of its 
uniqueness, described in some detail, it probably represents only 
one of several methods by which a basal bulb may arise. It 
can hardly be doubted that the original basal bulb of a hydranth 
develops directly from the basal-disc or ‘‘ Fussplatte”’ of the 
larva, and development from a lateral bud seems to be hinted at by 
the following facts. : 
In many cases there are two basal bulbs at the base of a single 
hydranth (see pl. xxx, figs. 2 and 3) and in such case they arise 
not in linear succession but one terminally and one laterally. 
