POLYPI. 131 



ceivecl the polypes alive in the vesicles of the denticulated class of 

 corallines, and particularly in this" — now the Sertularia pumila : 

 — " these animals are of a much lai-ger size in the vesicles than 

 those in the denticles."* In another species {Campanularia di- 

 chotomn) he figures " the young polypes coming out of the vesi- 

 cles, but still adhering to the umbilical chord." Dr. A. Farre has 

 seen the development of the germ-masses, which are included in 

 a delicate membrane and extend along the axis of the germ-vesi- 

 cle, in the same Campanularia : the germs are covered by a cili- 

 ated epithelium ; they then become bell-shaped medusas, with mar- 

 ginal tentacles, and escape swimming freely. Mr. Lister's figures 

 h 5 and b 6|-j- show the little medusoids escaping from the germ- 

 vesicles of the Campaiiularia dichotoma ; but they are represented, 

 as Ellis described them, as polypes. Abundant evidence has been 

 afforded, especially by Dalyell, that Ellis did not, as Dr. Grant has 

 stated I , commit the error of mistaking mere ciliated locomotive 

 gemmules or ova for young polypes. In many Sertularics, as Dalyell 

 has shown, the young quit the germ-vesicles as locomotive ciliated 

 animalcules, like Planarite, which move not only by the ciliaj but by 

 a general contraction of the tissue. This kind of larva, which he 

 calls " planula," crawls rather than swims, and in twenty-four hours 

 presents the appearance of a disc with a series of peripheral rays ; it 

 then settles, expands, and a stem shoots up, developes a polype, and 

 thus a new hydrozoal individual is generated. This metamorphosis, 

 first observed and described by Cavolini § in the Sertularia racemosay 

 has been illustrated with accurate and minute details by Loven. || 



The more remarkable phenomenon of the medusoid form of larva 

 is best shown in the claviform Corallines, and has been especially 

 described by Loven^, in an excellent Memoir on the Syncoryne 

 ramosa of Sars, and by Steenstrup in the Coryne Fritillaria.** This 

 species originally developes a many-armed nutritive polype, or 

 individual ; but retaining many unchanged germ-cells, these, by the 

 stimulus of the excess of nutriment, begin to repeat the process, and 

 push out buds in an analogous position to that in the Hydra fusca^ 

 viz., around the base of the stomach of the first, or parent animal ; 

 but the buds, instead of repeating the form and condition of that 

 animal, take on a higher form, resembling that of a bell-shaped 

 Medusa ; they become detached and swim off to a distance, forming 



* XCVII. p. 10. pi. V. A. also p. 21. and 23. pi. xxxv-iii. fig. 3. B. 

 t CVII. pi. X. X CXIX. p. 54. 



§ CVI. p. 2G1. tab. vi. || CXII. tab. vi. figs. 14—17. 



t CXII. ** XCIII. 



K 2 



