ANTHOZOA HYDROIDA. 21 



such mechanism as we have described, been carried to a dis- 

 tance, and spread over the bosom of the deep. 



There are many facts which prove that the growth of these 

 polypidoms is very rapid, but not more so than might be anti- 

 cipated when it is remembered how vast is the number of 

 polype architects ; and no sooner is a new branch extended 

 than it becomes almost simultaneously a support of new 

 workers, which, with " toil unweariable," add incessantly to 

 the materials of increase.* Their duration is various : some 

 have only a summer's existence, as Laomedea geniculata ; 

 many are probably annual ; and the epiphyllous kinds cannot 

 at most prolong their term beyond that of the weed on which 

 they grow : but such as attach themselves to rocks are pro- 

 bably less perishable, for their size and consistency seem to 

 indicate a greater age : it is thus with the Tubularite and 

 some of the compound Sertulariadse.f 



* " In the S. polyzonias, I have some reason to believe that a large specimen can be 



formed, under favourable circumstances, in the course of fourteen days." Couch, Corn. 



Faun. iii. p. 8. 



t Couch, Corn. Faun. iii. p. 9. That the polypidoms of the Hydroid Zoophytes 



perish soon after attaining their full size, is rendered probable by the fact of their being 



cast ashore, some at one season and some at another, independent of storms or any 



cause that could tear them away from their attachments. As an illustration, I give in 



this note some facts of the kind communicated to me by Miss Forster, who made the 



observations at Tynemouth, Northumberland, from the middle of July until the end 



of November, 1839. 



TUBULARIA INDIVISA thrown on shore plentifully in August ; occasionally in 

 September, October, and November. 



TUBULARIA LARYNX the finest specimens in August, but found afterwards. 



TUBULARIA RAMEA common in August and September. 



THOA HALECINA one very fine specimen, crowded with vesicles, in July ; inferior 

 specimens with vesicles in August, and very poor pieces afterwards. 



THOA MURICATA plentiful in November, crowded with vesicles. 



SERTULARIA POLYZONIAS in August specimens found on the shore were about half 

 an inch high, but two dredged from deep water were about two inches : in Novem- 

 ber pieces found on the shore were from two to fully three inches high. Vesi- 

 cles, sparingly produced, were found in August and November. 



SERTULARIA RUGOSA vesicles plentiful in July and August ; very fine, but without 

 vesicles in October and November. 



SERTULARIA ROSACEA vesicles in July, August, September, and November. 



SERTULARIA PUMILA vesicles in August and September. 



SERTULARIA PINNATA in August this species was dredged up from deep water, but 

 it was not found on the shore until November, when the specimens were much 

 larger : no vesicles at either time. 



SERTULARIA TAMARISCA only one small piece, with two vesicles, in July. 



