Chap. II. 



MORPHOLOGY AND NOilENCLATURE. 



83 



yet, 80me of those Ilydite — Ilydractiiiia, for instance — produce only male Medusas 

 buds, and others only female Meduste buds, and in this genus the individuals 

 producing either niide or female Medusce buds form distinct communities. Again, 

 not all Medusa^ are fertile ; for instance, the so-called swimming-l>ells of the Diph- 

 yida) and Siphonophora^, though evidently medusoid in their structure, have neither 

 male nor female organs. 



After this digression, which was indispensaljle as an introduction to a critical 

 survey of the prevalent nomenclature of the Acalephs, let us now consider the 

 different names under which the different elements forming the communities of the 

 Siphonophora5 have been described, that we may hereafter more readily compare 

 them with the other members of the class ; for the chief difficulty in harmonizing 

 the nomenclature of the Acalephs arises from the complication of the names applied 

 to the Siphonophora\ In these communities we have at first to distinguish the 

 medusoid and the hydroid individuals, in the same manner as among the Ilydroids 

 proper ; and, to do this with accuracy, we must recall the comparison already made 

 (p. 50) between Siphonophora^ and Hydroids as compound communities, and remember 

 the pi-evalencc of polymorphism in most of these animals. 



The extensive investigations of Leuckart, Vogt, Kolliker, Gegenbauer, and Huxley 

 upon Siphonophoiw, and the many species now known in all their stages of growth, 

 furnish the most welcome materials upon whicli to Ijase further comj^arisons. The 

 young Velella, as described and figured l)y Huxley (Oceanic Ilydrozoa, PI. XL Figs. 

 9 and 14), is unquestionably a simple genuine Hydra, provided at first with only 

 few tentacles, and in that condition comparable to any single head of a common 

 Hydroid freed from its stem. An adult Velella, on the contrary, is a Hydrarium, 

 that is, a community of secondary Hydras grown up l^etween the actinostome and 

 the tentacles of the primary Hydra, and from which in due time genuine Medusa; 

 buds arise. The presence of a shield with a crest in the disc or Ijell of the 

 primary Hydra is only a structural peculi- p;^_ 43. 



arity of that animal, but not any more 

 altering its true nature and affinities, than 

 the presence of a shell in the mantle of a 

 Gasteropod. The enlarged primary Hydra 

 of the Velella community, when it has 

 become a complicated floating apparatus {Fig. 

 47) from which hang numerous fertile Hy- 



Single so-called fertile tcn- 



dra, the so-called fertile tentacles, — " gono- tacie of 



IT J- T 1 -r> 1 • 1 TT Vfxelt^a mutka, Bosc, 



blastidial Polypites' oi Huxley, "individus Bearing 5Mus« imd. </,/.- a 



ij ^T £* '^T 1 cc *1'1 T\ ^ f^ r* ~r i; Base of attachment. — b Blunt 



reproducteurs ot V ogt, peripherische Polypen of Leuckart, ,.„a „f the tentacle, as it 

 "kleine Polypen" of Kolliker {Fig. 48),— is still as much a Hydra :rrr "'" '"' ""°"" "' 



Fi(j. 47 



Velella mutica, Bosc. 

 n So-called mouth, —aa So-raUed 

 tentacles. Between the sterile 

 tentacles and the mouth arise 

 the secondary Hydrae. or so- 

 called fertile tentacles, the p:ouo- 

 blaatidial Polypites of lluxley. 



