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follows tug, these spasmodic efforts alternating with long 
periods of quiescence, until at last the connecting link sud- 
denly gives way, and the medusa drops into the water. 
Before we finally dismiss it from the colony, and while it 
still continues an integral portion of it, let us pause to consider 
the somewhat perplexing question of individuality with re- 
ference to these composite organisms, in which many zooids, 
similar and dissimilar, continuous and discontinuous, are the 
product of a single ovum. 
Philosophically regarded, the whole senes of forms evolved 
by budding, and intervening between two generative acts is, no 
doubt, the equivalent of the “ individual ” in other classes ; 
and this is the case, even if some of these zooidal forms detach 
themselves, and lead an independent existence. In this sense 
the polypite and the medusa are as undoubtedly not “indi- 
viduals.” Yet it must be accounted unfortunate that this 
term should have been applied to the zoological conception. 
It would be better, surely, to speak of the life-series of the 
zoophyte, of which the various zooids are so many units, with 
the understanding that this corresponds with the “individual ” 
of other tribes, than to perplex the ordinary mind by asserting* 
that the free and independent medusa is not an individual 
at all, but that a hundred polypites and a company of a 
hundred medusse together constitute an individual ! The 
medusa is not the immediate and single product of an egg. 
It is developed as a bud from another structure, which is the 
immediate product of the ovum. It is not, therefore, an 
“ individual,” biologically considered. But in the ordinary 
sense of the words, as Professor Allman has remarked,* “ every 
zooid has an individuality of its own,” which it is important ter 
recognize. The medusa, with its original and distinctive 
manner of life, and its independent ways, has a very marked 
individuality of its own, which I shall endeavour to exhibit in 
the following pages. 
To resume the history, the liberated medusa after a brief 
period of quiescence begins to move rapidly through the 
water, propelling itself by the alternate contraction and ex- 
pansion of the gelatinous disc or swimming-bell, which consti- 
tutes its most striking feature. It certainly presents a remark- 
able contrast to the sedentary kindred from which it has lately 
parted company. Its whole organisation fits it for active loco- 
motion, the polypite is rooted to one spot for life ; is a restless 
floater, ranging widely through the waters of the sea, the latter 
is a fixture : it pursues its prey, the latter waits for it ; it is 
mercurial, the latter vegetative ; and yet after all it is but a 
* In his great work on the “ Tubularian Hydroids,” 1871.' 
