ACALEPHS IN GENERAL. 



Part I. 



Fl,j. 29. 





Bunch of MeJusa' of 

 Physalia Akethusa, Til. 

 Ill various stages of Jevelop- 



raeut. 



a Common hollow base of attach- 

 ment of the whole bunch, com- 

 municating with the cbyniiferous 

 cavity of the air sac. — fj 8o-calleJ 

 Polyp, or sucker. — d cl d d The 

 Meaus;e liuas. 



linncli of JIoilusio of 



TUBULARIA CoUTHOUYI, Ag. 



a ('ommon axis. — d d d Mature 

 Medusje, alreatiy withering. 



with the hirger so-called Pohps, and smaller ones connected with the smaller indi- 

 viduals {Fig. 28 c c). These two kinds of individuals seem to be always distinct, and 

 some of them never even gape at their outer end. The individuals of these two 

 kinds form large clusters, small communities as it Avere, connected Avith the larger 

 community. There is a third kind of individuals, smaller than either {Fir/. 27 d d), 

 Avhich are fertile, and upon the neck of which arise numerous Meduste buds, pre- 

 senting all the characters of the naked-eyed Medusa^; that is, having, like them, 

 four radiating tubes and a circular tube [Fig. 2!> d d). The.^e Medusa* form clusters 

 so similar to the bunches of Medus:e that 



Fin. 30. 



hang from the genuine Tubularia, that they 

 might easily be mistaken one tin- the other 

 [Flu. 3(1). (Compare PI. XXIV. fig. 1 with 

 Fl(j. 2!).) Here, then, is a Sijihonojihorous 

 comnmnity, in every respect similar to a 

 Il^droid community, consisting of various 

 kinds of Ilydroids. from some of which are 

 produced MedusfO buds, as in ordinary Ily- 

 droids. The fact that in Physalia these Meduste bnds do not 

 se^iarate from the community liut Avither upon the stock from 

 Avhicli they arise, is not peculiar to this group of animals; since 

 Ave have already seen, that, in the family of Tulnilariiv, Ave have those that produce 

 free Medusa*, the genus Hyliocodon and others, the genera Tubularia {Fii/. 30), 

 Thanniocnidia, and Par_\pha, the Medusa of Avhich do not separate from their 

 jiai'out stock. These facts are in themselves sullicient to show that the Physalia 

 community does not consist of au'ti'rcii'ated Polviis, but of auu'reji'ated IlA'droids : and 

 that iu a natural classification they cannot lie referred to any other order than the 

 Hydroids, though in that order they constitute a distinct family. 



The idea, of considering the Medusa buds of these couununities as the sexual 

 organs of the Ilydroids is not admissilile ; for Avt; haA'e seen that these liuds may 

 become independent and free, and that in due time they actpiire themselves distinct 

 se.xual organs, some individuals lieing proA^ded Avith ovaries the eggs of Avhich 

 ruidergo all the changes through Avhich ordinary eggs jiass until ncAV individuals are 

 formed in them, Avhile other individuals are jirovided Avitli sjiermaries Avhich at the 

 time of spawning are fdled Avith spermatic particles. Now, unless sexual organs 

 can themselves have distinct sexual parts of Ijoth sexes, all these so-calleil sexual 

 organs of the Hj'droids must lie considered as naked-eyed Medusa>, Avliich are not 

 freed from their parent stock as is the case Avith others. 



Velella and Porpita consist of compound connnunities like Physalia, only that 

 here the diversity of the Ilydroids attached to a common base is not so great, 



