POLYPI. 131 



ceived tlie 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 larger size in the vesicles than 

 those in the denticles."* In another species {C amp anul aria di- 

 chotoma) 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 medusae, with mar- 

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

 b 5 and b 6jf show the little medusoids escaping from the germ- 

 vesicles of the Ca^npanidaria dicJiotoma ; 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 J, commit the error of mistaking mere ciliated locomotive 

 gemmules or ova for young polypes. In many Sertulari<B, as Dalyell 

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

 animalcules, like Planarioe, which move not only by the cilia^ 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. xxx%-iii. fig. 3. b. 

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



§ CVI p. 261. tab. \i. II CXII. tab. vi. figs. U— 1 7. 



t CXII. ** XCIII. 



K 2 



