562 Records of the Indian Museum. [Vou, aaa} 
The special resemblances to Gonionemus buds are slight and of 
little account. In both the buds seldom occur more than one at 
a time on a polyp; and in both it seems that the usual polarity of 
hydroid buds is reversed, and that the free end becomes the area 
of attachment, and the attached end the oral and tentacle-bearing 
area. It may possibly be that this remarkable inversion of the 
general mode of hydroid development is not a regular habit, but 
simply emphasises that in hydroid buds there exists an indeter- 
minate polarity ready to be determined by external physical con- 
ditions. Such has been shown experimentally to characterise the 
adult stems of forms like Tubularia and Corymorpha, or in closer 
analogy exists in the larva of Corymorpha. It is likely that here 
as in these larvae ‘‘ external factors such as contact and possibly 
gravity determine the kind of structure (e.g. hydranth or holdfast) 
which will ultimately appear in connection with the area of 
differentiation. ‘That is they determine the polarity of the adult.” 
(Torrey, 1907, p. 292). 
ANALOGUES OF THE BASAL BULB. 
The normal organs of attachment of the vegetative stocks of 
the Hydrozoa fall into two broad classes: (1) those in which the 
base of the hydranth is simply modified into a fleshy disc or cylin- 
der, occasionally naked, more often covered by a mucous secretion 
in which foreign debris becomes embedded, or rarely enclosed in a 
membranous film of chitin; (2) those in which a more specialized 
structure is apparent, the attachment being due to well-defined 
root-like strands of coenosarc, enclosed in a distinct coat of peri- 
sarc (the stolon or hydrorhiza) and forming simple threads, or 
branched ‘‘ roots,’ or anastomosed networks, or even thick skele- 
tal layers (as in Hydvactinia). 
It seems to me that these two types of hydroid attachment 
are homologous, that the simple fleshy attachment was the direct 
forerunner of the hydrorhiza, and may be regarded as a primitive 
characteristic in those forms in which it occurs. In known species 
of Hydroids it is possible to trace the steps by which the simple 
basal disc became branched and split to form a root-like organ, 
and by which the final complexity of the hydrorhiza was built up. 
A process parallel to that suggested by a survey of the attach- 
ment organs of adult hydroids seems to be followed in summary 
during the development of certain individuals. One need only 
point to the early life-history of the colonial form Eudendrium 
vamosum, after the planula has relinquished its free state and 
settled down, to illustrate the development of a facsimile of the 
basal disc into a complex hydrorhiza (see Allman, 1871-72, pl. xiii, 
figs. 12-16 and 2). 
It would be out of place, however, to develop a thesis of the 
evolution of the hydrorhiza in this paper, and I shall merely indi- 
cate the forms which seem to stand most closely related to our 
Indian species as regards their mode of attachment. 
