. The Annals and magazine of natural history; zoology, botany, and geology . to a gonoblastidium, and this to a gono-blastocheme, which in its turn developes, by a similar non-sexual act, the sexual bud or gonosac. The form of the dia-gram of Geryonia, however, differs from that of Campanularia,inasmuch as Campanularia presents a simple linear series,while in Geryonia, in consequence of one and the same zooid(the Geryonidan) producing two sets of heteromorphic buds(the gonosac and the iEginidan), we have a series present-ing two branches, which run off in different , however, is
. The Annals and magazine of natural history; zoology, botany, and geology . to a gonoblastidium, and this to a gono-blastocheme, which in its turn developes, by a similar non-sexual act, the sexual bud or gonosac. The form of the dia-gram of Geryonia, however, differs from that of Campanularia,inasmuch as Campanularia presents a simple linear series,while in Geryonia, in consequence of one and the same zooid(the Geryonidan) producing two sets of heteromorphic buds(the gonosac and the iEginidan), we have a series present-ing two branches, which run off in different , however, is exactly what occurs in Hydractinia echinata,pi which the gonosac is borne not only on a gonoblastidium,but also occasionally on the trophosome directly *. Thiswill be at once obvious if the diagram just given be com-pared with the following, which represents the alternation inHydractinia, and in which the symbol GB is used to indicatethe gonoblastidium. It will then be apparent that the two haveprecisely the same form. T + Gon|- +GB +Gon T+Gon|0 T + Gon GB +Gon +GB +Gon. © GB +Gon T + Gon GB +Gon © &c. &c. &c. &c. * As pointed out by Dr. T. Strethill Wright (Proc. Roy. Phys. Soc. ofEdinb. Nov. 1856). 474 Prof. Allmau on the Hydroida. While Haeckel has thus done good service to our knowledgeof the Hydroida in pointing out a genetic relation between theJEginida and the Geryonidce, his labours have been at least asvaluable in showing that the structure of the JEginidce, is in allessential points identical with that of the Geryonidce. He hasproved, for example, that the circular marginal canal, hithertodenied to the JEginidcB, is really present; and there can accord-ingly no longer be any difficulty in placing these Medusas in thesame group with the rest of the Hydroid or gymnophthalmicforms*. It cannot, however, be overlooked that the position of theiEginidan buds is remarkable and anomalous; for they are-borne by the solid tongue-like process which in Geryonia pro-jects
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