lOG MORPHOLOGY. 



form from the Inicldcr, and lias, at the same time, preceded it in the line of succession. Thus, 

 true hydranths are never emitted either by blastostyle, blastochemc, or gonophore ; and to this 

 law the peculiar gemminatc hydriform bodies which are found on the summit of the female blas- 

 tostyle in certain species of Halecium form no exception ; for though closely resembling true 

 hydranths, they appear to have a difTerent signification, contributing rather to the generative 

 functions of the hydroid, while they have no power of continuing the succession either in a direct 

 or collateral line like the proper hydranths of the trophosome. 



Now, a glance at any of the formulae given above renders it evident — 1. That between every 

 two acts of true generation there are interposed one or more acts of non-sexual multiplication. 

 2. That the heteromorphic elements in each recurring period of the succession are invarialily con- 

 nected with one another by a non-sexual and not by a sexual genesis. 3. That the type of 

 heteromorphisra exactly repeats itself after each true generative act. 



A still further fact, however, is apparent in all the cases here adduced, namely, that a certain 

 number of zooids, incapable of attaining to sexual maturity, and hence becoming multiplied only 

 by zooidal reproduction, occur in every succession. To the universality, however, of this prin- 

 ciple, Haeckel regards the case of the Geri/onidcR already referred to (p. 82), as affording an 

 exception. He has found Geryonidan medusae swimming freely in the open sea, in such an early 

 stage of their development, that he believed them to have been produced by the direct develop- 

 ment of an ovum, and yet these medusae have been traced by him into a condition which he 

 regards as that of sexual maturity, in which state they not only produce generative elements, but 

 give origin, by heteromorphic budding within the stomach, to ^ginidan medusa {Cunina), these 

 Cuiiina-hwA?, also attaining to a condition of sexual maturity. 



These facts are regarded by Haeckel as presenting an entirely new type of genesis — a 

 type totally different in its fundamental principles from the phenomena hitherto included under 

 the head of " Alternation of Generations ;" and, believing a new term to be needed for it, he pro- 

 poses to distinguish it by the designation of " Alleogenesis." It is worth while to inquire 

 how far Haeckel is borne out in this mode of viewing the phenomena of Geryonidan 

 development. 



Admitting that Haeckel is right in regarding his Geryonidan as developed directly from the 

 egg without the intervention of a non-sexual trophosome, I am by no means prepared, as I have 

 elsewhere^ stated, to take for granted the proper sexuality of this medusa. On the contrary, I 

 am still disposed to consider the sexual pouches of the radiating canals as truly zooidal deve- 

 lopments corresponding, notwithstanding their flattened leaf-like form, to the more prominent 

 pouches developed on the radiating canals of such forms as Obelia ; so that, in accordance with 

 this view, the Geryonidan medusa would be a true blastocheme. If this be so, then the non- 

 sexual character of the Geryonidan must be admitted, and a non-sexual element will thus 

 become intercalated in the series, even though the hypothesis of a non-sexual hydi'iform tropho- 

 some be given up. Haeckel, it is true, referring to my view of the zooidal nature of the sexual 

 pouches of Geryonia, argues against it, and states his conviction, from personal examination of 

 these pouches, that they are simple lateral dilatations of the canal, with the generative products 

 developed out of the epithelium of their walls.^ 



' ' Ann. and Mag. of Nat. Hist.,' 1865. 



* Haeckel, 'Die Familie der Riisselquallen. Vorwort,' vii. 



