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tlieir analogue the flower ; but, so far, can neither trace their 
lineage, nor follow the fortunes of their offspring. These un- 
attached medusae are mere fragments of a life-history ; they are 
like a few exquisite lines from a lost poem, which make us long 
to recover the missing context. 
Perhaps an apology is needed for isolating one element of 
the Hydroid, and treating of it apart from the individuality 
to which it belongs. But inasmuch as the medusiform zooid 
detaches itself altogether, at a certain stage, from the colony 
that has reared it, and thenceforth leads a perfectly independent 
and original life, with marked characteristics of its own ; 
and further, as it is the representative of one grand department 
of the hydroid economy, it seems permissible, as it is certainly 
convenient, to make it the subject of a separate study. We do 
not quarrel with a paper on flowers, apart from the plants that 
hear them, nor do we resent it as a sin against scientific accu- 
racy. Besides, as I have just mentioned, a large proportion 
of the hydroid medusse are still without pedigree, and must be 
treated provisionally as isolated beings. 
A hydroid colony (for associated life is the rule of the order) 
consists of at least two classes of zooids. They may not both 
be present at any given time, just as leaves and flowers are not 
always found together on the plant, but they are both essential 
elements of the perfect commonwealth. One class is charged 
with the alimentary, the other with the reproductive function. 
Both are evolved in the same way, as buds from the common 
substance of the zoophyte. The polypites or feeders of the 
colony are always permanently attached to it ; the reproductive 
buds also often pass through their various stages in situ , and 
wither away, like the seed-vessel on its stalk, after the libera- 
tion of the ova. But in many cases they take on a more 
highly specialised form, and are equipped for a free and loco- 
motive existence. Assuming a medusan guise they part from 
the sedentary colony, and exchange their vegetative ways for 
the customs of a vagrant life. The structural elements of the 
polypite are modified and readjusted in the free zooid ; the 
tentacles, which had only served for prehensile purposes, are 
webbed so as to form a contractile float, and the zoophyte which 
in its alimentary phase is the most vegetative of animals, 
appears, in its higher reproductive phase, as a restless ocean- 
wanderer. 
Let us take up the history of the so-called medusa, the 
w swimming polypite,” the reproductive member of the hydroid 
colony, at the point when it is about to cast itself loose, and 
enter upon its proper work of maturing and diffusing the winged 
embryos that are to perpetuate the species. The sexual buds of 
the zoophyte are borne in various positions; sometimes they 
