20 



OVUM. 



Fig. 15. 



Campanularia geniculata (A and R from Loven, us 

 copied by Steenstrup). 



A, modified or bell-shaped polype head or cap- 

 sule, producing the female individuals at g,ff,g ', the 

 earliest of these budding from the granular stem g'. 



B, the female heads expanded from the bell : one 

 of them containing two ova, o o ; the other con- 

 taining two ciliated embryoes, of which one is issu- 

 ing at the summit of the attached medusoid, e e. 



c (from Schultze), male heads of the same spe- 

 cies of Campanularia ; p, upper part of the polype 

 head, or bell-shaped capsule; c, sexual capsule, or 

 modified attached Medusoid, containing spermato- 

 zoa ; c', another of the same, burst, and spermatozoa 

 discharged, s ; c", other spermatic capsules advanc- 

 ing behind the first. 



ledge of Desor's observations, and has farther 

 proved the necessity of fecundation for the 

 development of the ova so produced in the 

 Campanularia geniculata (see fig. 15. C.). 



The various modes of production as they 

 have been observed in the Tubularia by Van 

 Beneden*, have been so fully detailed in the 

 Article PoLVpiFERA,that the reader is referred 

 to that article for an account of them. But 

 it is to be observed that the reconversion of 

 the Medusoid progeny of this animal into the 

 Polype form described by that author (see 

 Article POLYPIFERA,^. 50., p. 45.), has not 

 received confirmation from the researches of 

 other naturalists. 



Much remains still to be learned of this 

 remarkable process ; but enough has been 

 ascertained to show that in a certain number 

 of animals, usually known as passing the 

 greater part of their lives in the Compound 

 Polype condition, the state of sexual com- 

 pleteness frequently belongs not to the Polype, 

 but to a progeny having the form of a Medusa, 

 and produced by a non-sexual process of de- 

 velopment from the Polype stem. 



AculephfE. Some time before the peculiar 

 history of the development of the Polypina, 

 now sketched, was discovered, an equally 

 curious and unexpected phasis in the genera- 

 tion of some Acalephae or Medusae had been 

 established by the concurrent researches of 

 several inquirers ; by which it was shown that 

 the animals familiarly known as sea nettles 

 existed for a time in the early stages of their 

 development in the form of an attached poly- 

 poid, and were produced by a process analo- 

 gous to gemmation, or transverse fission, in 

 numbers from this Polype stock, j- 



Adult Medusae are perfect animals in which 

 the male and female sexual organs are placed 

 on distinct individuals. The fecundated ova 

 which they produce are first developed into a 

 ciliated moving animalcule somewhat like a 

 polygastric infusorian. This creature, after 



" Mem. de 1'Acad. de Bruxelles, torn. xvii. 



t The Swedish naturalist Sars appears to have 

 taken the lead in this discovery, as earl}- as 1828, by 

 his observation of the Compound Polypoid, from 

 which the Medusas are thrown oft'; and subsequently, 

 in 1835, by the discovery that this animal, or stro- 

 bila, is really the young condition of a Medusa, or 

 rather a colony of Medusae. Very interesting obser- 

 vations of a similar kind were published by Dalzell 

 on this body, under the name of Hydra tuba, in 1836, 

 but his observations probably date from an earlier 

 period (Edin. New Phil. Journ. vol. xxi. 183G). 

 Sars pursued the investigation of the process further, 

 and published the results in Wiegmann's Archiv, 

 1837 ; but the complete account of his observations 

 was not published in the same Journal till 1841 ; see 

 also Ann. des Sc. Nat. for 1841. In the meantime V. 

 Siebold had arrived at precisely similar conclusions, 

 and subsequently their views have been fully con- 

 firmed by Dalycll (Kemarkable Animals of Scot- 

 land) ; J. Reid (Ann. of Nat. Hist. 1848, and Phy- 

 siolog. Researches) ; Steenstrup (Alternations of 

 Generation) ; and Huxley (Phil. Trans. 184!>, part 

 ii.) See also Dujardin, Mem. sur le Developpement 

 des Merluses et des Polypes Hydraires, Ann. des Sc. 

 Nat. 1845. The reader is also referred to Dana's great 

 work on Zoophytes in the United States Explor- 

 ing Expedition. " Philad. 1848. 



