136 
Z. HYDROIDA. 
Sertularia. 
and the same specimen, that the young- vesicles had long spines at 
their tops, the more mature shorter ones, and on full-grown vesicles 
they were nearly or altogether obsolete ; while bluntly tubulous and 
acutely pointed cells occurred promiscuously, on the same stalk, in 
specimens of every size and exterior habit. Linnaeus, apparently 
swayed by these assertions, followed Pallas ; but Ellis, in a later 
work, adhered to his first opinion, for, “ besides the difference of their 
denticles (cells) and ovaries,” which he evidently regarded as per- 
manent, they have, he says, “ quite a different habit and manner of 
growing.” All subsequent writers have assented to Ellis’s views, 
most of them, at the same time, expressing a suspicion of their cor- 
rectness, and my own limited observations have possessed me with 
the same dubiety. Specimens can be readily produced which, from 
habit and the figure of their cells, will be at once pronounced the re- 
presentatives of distinct species, but a larger examination may lead to 
another conclusion. I have seen no specimens of S. cupressina 
with the cells of S. argentea, * but I have seen several which, from 
their habit, 1 would refer to the latter, with the cells and vesicles of 
the former. Such a specimen is figured in Plate XII. I can also state 
that on the same specimen I have observed cells that might be con- 
sidered as belonging to either species ; and with these facts I should, 
perhaps, have amalgamated the synonymes, had I not been aware 
that some of our best naturalists, for example Bean and J. V. Thomp- 
son, are opposed to the junction. “ Besides,” to adopt the words of 
Professor Lindley in a somewhat similar discussion, “ our daily ex- 
perience shows us that excessive analysis is far preferable to excessive 
synthesis, especially for the purposes of students; the former leads 
to no other inconvenience, than that of increasing the degree of in- 
vestigation which species must receive to be understood : the latter 
has a constant tendency to render investigation superficial, and cha- 
racters confused,” Syn. of the British Flora, Pref. p. ix. 
Professor Jameson has inserted Sertularia cupressoides 
among those species found in the Frith of Forth, Wern. Mem. i. 
564 ; and in the work entitled “ Corallina,” p. 83, the elegant Aus- 
tralasian S. elongata and S. pectin ata are said to be found on 
the English coast. I believe there is some error in all these in- 
stances. 
I have repeatedly observed on oyster-shells, and among the roots 
* It deserves to be remarked, in connection with this point, that the charac- 
ters of S. argentea given by Lamarck are really those of S. cupressina j and 
this has ascribed to it the diagnostics of S. argentea. 
