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 possessel 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, I 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- 

 ti'alasian S. elongata and S. pectinata 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 ; and 

 this has ascribed to it the diagnostics of S. argentea. 



