IgI5.] J. Rircui1e: Hydrotrds of the Indian Museum. 565 
terminal section of branch or stolon, as in several Campanularians 
and Plumularians (Billard, 1904, p. 41 et seq.) to vital processes 
such as the exaggerated ‘‘decapitation”’ of Moertsia or the me- 
dian division of Hydra or Protohydra. 
So far as I am aware, transverse fission in a determinate 
region of the base of an adult individual, is a normal mode of 
multiplication in only one hydroid species other than Annulella 
gemmata, Even that solitary case differs from Annulella: for in 
Hypolytus murbachit the fission takes place near the proximal end 
of a distinct hydrocaulus; it proceeds gradually by means of con- 
striction, but without any disappearance of ectoderm (so far as 
one. can judge) so that there are set free successive small naked 
planula-like segments which, after more or less limited wandering, 
settle down and develop directly into new hydranths (Murbach, 
1899). In Hypolytus a wandering ‘‘ blastolyte’’ escapes from a 
free adult; in Annulella a wandering adult escapes from an at- 
tached basal section. 
In this respect Annulella comes very near to the hypothetical 
form postulated by Murbach as a precursor of Hyfolytus (Mur- 
bach, 1899, p. 353); but to me there appears to be no close re- 
lationship between the two forms. 
The phenomena of transverse fission in Annulella naturally 
bears a general resemblance to other well-marked cases such as the 
strobilisation of Moerisia (Boulenger, 1908, p. 364) or the division 
of Protohydra (Chun, 1894, p. 217). But the transverse fission of 
Annulella stands by itself as regards the structural changes in- 
volved (such as the disappearance of ectoderm at the neck, paral- 
leled only in the sporosacs of Dicoryne), and as regards. the final 
results, since here a segment specially modified with a view to 
fission remains attached, while the hydranth which gave it origin 
escapes. 
SYSTEMATIC POSITION OF ANNULELLA GEMMATA. 
The majority of the outstanding features of Annulella gem- 
mata are primitive in character, a few seem to be adaptive. 
Among the latter may be reckoned the annular arrangement of large 
cells upon the tentacles (see p. 558), the great length of the ten- 
tacles themselves, and the adoption of basal transverse fission. All 
of these bear upon the free-living stage, the last as the means of 
attaining freedom, the former as adjuncts to a (supposed) pelagic 
existence. 
The primitive characters include the normal adoption of 
various types of vegetative budding ; but even these are of simple 
nature. Thus the setting free of minute, non-tentacled, planula- 
like buds must probably have preceded in evolutionary develop- 
*ment even the liberation of buds at a miniature adult-stage, as 
occurs in Hydra and occasionally in Moerisia, both of which are 
included in the family Hydridae. Further, the naked basal disc 
observed in one young specimen of Annulella appears to be homo- 
