Chap. I. ALTERNATE GENERATIONS. 91 



that this l)rooil originating from eggs, may increase and mnltiply hy producing new 

 individuals like themselves (Syncoryne), or of two kinds (Campauularia), or even indi- 

 viduals of various kinds, differing all to a remarkable extent, one from the other. 

 (Hydractinia,) but in neither case resembling their common parent. None of these 

 new individuals have distinct reproductive organs, any more than the first indi- 

 viduals l»()rn from eggs, their multiplication taking place chiefly by the process of 

 budding; but as these buds remain generally connected with the first indi\idual 

 born from an egg, they form compound communities, similar to some polypstocks. 

 Now some of these buds produce, at certain seasons, new buds of an entirely differ- 

 ent kind, which generally drop off from the parent stock, at an early period of their 

 development, (as in Syncoryna, Campanularia, etc.,) and then imdergo a succession of 

 changes, which end by their assuming the character of the previous egg-lajang 

 individuals, organs of reproduction of the two sexes developing meanwhile in them, 

 which, when mature, lead to the production of new eggs; in others (as in Hj'drac- 

 tinia.) the buds of this kind do not drop off, but fade away upon the parent stock, 

 after having vmdergone all their transformations, and also produced in due time, a 

 number of effs»} 



CO 



In the case of the Medusje proper,^ the parent \axs eggs, from which originate 

 polyplike individuals; but here these individuals divide by transverse constrictions 

 into a number of disks, every one of which undergoes a succession of changes, which 

 end in the production of as many individuals, each identical with the parent, and 

 capable in its turn, of laying eggs, (some, however, being males and others females.) 

 But the pol3'plike individuals born from eggs may also multiply by budding and 

 each l)ud undergo the same changes as the first, the base of which does not die, but 

 is also capable of growing up again and of repeating the same process. 



In other classes other phenomena of a similar character have been observed, 

 which bear a similar explanation. J. Midler^ has most fully illustrated the alter- 

 nate generations of the Echinoderms; Chamisso, Steenstrup, Eschricht, Krohn, and 

 Sars, those of the Salpag ; * von Siebold, Steenstrup, and others, those of certain Intes- 

 tinal Wonns.^ 



This alternate generation differs essentially from metamorphosis, though some 



* I liave observed many other ooniliiiiations of a Sii)lionoi)liora, .see the works quoted above, p. C9, 



siniihir character among tlie Ilydroid Medusa-, which note 3. 



I .-iliall (hscrilie at f'ldl h-ngth in my second vohime ; ^ See Siebold, and Saus, ([. a., p. CO, note !). 



and to which I do not ailuch' liere, as they coukl not ' Mi'Li.K.it, (.!.,) Ueber den allgenieincn Phin, 



be unchM'stood without numerous drawings. Tlie etc., q. a., p. 7t), note 1. 



case of Ilyibaetinia is not quite correctly repre- * See the works, q. a., page 72, note 4. 



sented in the works in wliicli that aninial has been * See the works, q. a., page 76, note 2, and 77, 



described. Respecting Physalia and the other note 1. 



