62 HTDROZOA. 



cavity is formed throughout the central portion of 

 the mass. Even at this period the larva produces 

 free buds from its proximal extremity, 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, distally, 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 known as Medusidm are but the 

 free-swimming gonophores of various other Hy- 

 drozoa. Thus, from the ovum of Ttirris, 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 Bour/ain- 

 tillea Britannica, a common form of Medusoid, 

 is, in truth, the reproductive body of Atractylis 

 ramosa, one of the Corynidce, 



