DEVELOPMENT. 97 



Gosse^ has seen the medusa dcscrihcd by Forbes under the name of Tiirris nrr/lecln, discharge 

 from the generative mass formed in the walls of its manul)rium ciliated planuLnc, which, after 

 some time, fixed themselves to the glass, and became elongated into adherent, branched, stolon- 

 like bodies, which threw up a perpendicular stem, on whose summit a circle of four tentacles 

 was developed, and the whole became thus changed into a C7«jj«-like hydroid. 



Strethill Wright^ subsequently watched the development of the ovum in this same medusa. 

 His observations agree with those of Gosse, but he has succeeded in tracing the development a 

 step further; for he saw the tentacles increase in number by the growth of others behind 

 those first formed, giving by their scattered disposition a still more C/«u«-like appearance to 

 the hydroid, while he also noticed the formation of a chitinous periderm which clothed the 

 creeping stolon. 



Gegenbaur' describes the development of the egg in a medusa, which he names Lizzia 

 KulliJceri. He has seen the segmentation of the vitellus, and the formation of a ciliated planula, 

 which, after enjoying for a time its locomotive existence, loses its cilia, fixes itself to the side of 

 the vessel, expands one extremity into a disc of adhesion, elongates the rest of its body into 

 a cylindrical stem, which after clothing itself with a chitinous polypary, develops a mouth upon 

 its free extremity, and just below this throws out a verticil of tentacles, while the expanded base 

 becomes extended into short stolon-like prolongations. 



The development of the ova in another medusa, named by Kolliker Oceania armafa, was 

 also observed by Gegenbaur.* He traced the segmentation of the vitellus, the formation of a 

 ciliated planula, the fixation of the planula, and its development into a stolon-like body ; but 

 beyond this point his observations were not carried. 



Wright" noticed the occurrence of numerous planula^ which had made their appearance in 

 a vessel in which he had placed some isolated specimens of Thaumantias inconspicua, Forbes. He 

 believed that these planulae were produced by the Thaumantias, and he saw some of them fix 

 themselves to the sides of the vessel and develop a lobed disc of attachment. From this disc 

 arose a stem, which after developing from its summit a hydranth closely resembled the Cam- 

 panularia raridentafa of Alder. 



In the Zyyodactyla {^'Equorea) vitrina of Gosse, Wright^ also observed free ciliated planulse 

 to escape from the generative bodies, and, after fixing themselves to the sides of the vessel, 

 become developed each into a hydroid, with hydranth, hydrothcca, and perisarc, bearing, as he 

 informs us, a close resemblance to the Laomedea acuminata of Alder. 



Alexander Agassiz'' has followed the development of the egg in two forms of hydroid 

 medusa; — Melicertum campanula, Esch., and Tima formosa, Agass. In both he has seen the 

 formation of the ciliated planula, the fixation of the planula, and its gradual conversion into a 

 young campanularian trophosome. 



1 'A Naturalist's Katnbles on the Devonshire Coast,' 1853, p. 34<S, pi. 13. 

 ' 'Edinb. New Phil. Journ.,' July 1859, pi. 8, f. 1. 

 ' ' Generationswechsel,' 1854, p. 23, pi. ii, figs. 1-9. 

 ^ Loo. cit., p. 28, pi. 2, figs. 10— IG. 

 ° ' Micr. Journ.,' vol. ii, new ser. 

 ^ 'Micr. Journ.,' vol. ii, pi. iv, figs. 1 — 6. 



' 'Illustrated Catalogue of the Museum of Comp. Zool. at Harvard College,' No. II, pp. 115 

 and 134, 



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