G2 HTDROZOA. 



cavity is formed throughout the central portion of 

 the mass. Even at this period the larva produces 

 free buds from its proximal extremitj^, not more 

 than two appearing to arise at the same time, 

 though the process of gemmation may frequently 

 be repeated. Next, the distal region elongates ; 

 the nutrient cavity opens at its free extremity, 

 forming a mouth ; and thus a young polypite is 

 produced, while from the proximal margin two 

 new tentacula soon make their appearance. From 

 this region a rudimentary nectocalyx now arises, 

 a fold, in which are developed marginal bodies, 

 appearing, distal ly, in front of the tentacles, 

 between which four other tubercular lobes are 

 now seen to bud forth. The growth of the nec- 

 tocalyx slowly proceeds; eight marginal bodies 

 distinctly come into view ; the polypite diminishes 

 in size, finally becoming inconspicuous ; and the 

 animal attains the adult form characteristic of its 

 family, save only that reproductive organs have 

 not yet been observed. 



That instances of the above kind should be mul- 

 tiplied and re-observed seems, for many reasons, 

 very desirable, since, as already remarked, not a 

 few of the forms kno^vn as Medusidw are but the 

 free-swimming gonophores of various other My- 

 drozoa. Thus, from the ovum of Tarris, one of 

 the so-called genera referred to this order, a poly- 

 pite is produced, which sends forth a creeping 

 coenosarc, giving rise to a hydrosoma, clearly seem 

 to belong to the Corynidce {fig. 13). Dr. T. 

 Strethill Wright has further proved that Bougain- 

 'villea Britannica, a common form of Medusoid, 

 is, in truth, the reproductive body of Atractylis 

 ramosa, one of the Coo^ynidw. 



