THE ANNALS 
AND 
MAGAZINE OF NATURAL HISTORY. 
[THIRD SERIES. } 
No. 77.. MAY 1864. 
XXXV.—On the Construction and Limitation of Genera among 
the Hydroida. By Prof. Aruman, F.R.S. 
Ir will assuredly seem strange that those principles of classifi- 
cation which have been acknowledged as the only sound ones, 
and which have been our guide in the study of every other group 
of the animal kingdom, should be almost entirely ignored im our 
attempts at a systematic arrangement of the Hyprorpa. 
The cause of this, however, is sufficiently obvious. The indi- 
vidual Hydroid frequently presents itself in disconnected parts, 
which are very different from one another ; and it is only recently 
that the researches of zoologists have shown the mutual relation 
of these parts, and have demonstrated that organisms now en- 
_ jeying an independent life may have been at one time united in 
a single individual, and are at all times necessary for an adequate 
conception of it. So long, however, had the practice prevailed 
of regarding these component elements of the zoological indivi- 
dual as if they were entirely independent of one another, that 
even still we find it more convenient to treat them as such, to 
assign to them separate places in our systems, and record them 
under distinct generic and specific names. 
Yet this is totally at variance with the first principles of na- 
tural classification and of a scientific nomenclature; and the 
sooner we get rid of it the better for the harmony of biological 
method, and the progress of that department of zoology in which 
it has prevailed. 
For many years it has been known that a considerable num- 
ber of the fixed Hydroida give origin to buds which detach 
themselves from the fixed stock, and henceforward lead an in- 
dependent life in the open sea as free gymnophthalmic Meduse. 
The first who entertained, or at least gave definite expression to, 
the true relation between these two sets of elements in the 
Hydroid seems to have been Dujardin, when he compared the 
Ann. & Mag. N. Hist. Ser.3, Vol, xiii. 23 
