8 THE VOYAGE OF H.M.S. CHALLENGER. 



the various connected components of the broken up cormidia {Physalia, Agalmopsis, 

 and other Agalinidaj). This appearance is of the greatest interest, because, within one 

 and the same family {e.g., Agalmidas, Rhizophysidae), most nearly related genera exist, 

 of which one possesses perfectly ordinate cormidia, another completely scattered, and a 

 third an exact transition between these two. In this fact lies the direct morphological 

 evidence of the multiplication and dislocation of the portions of the Siphonophoral stock. 



DISLOCATION and MULTIPLICATION of ORGANS. 



If our medusome theory is correct, the title of real persons (or " individuals proper") 

 is only to be applied to those portions of the Siphonophoral stock which have originally 

 the morphological value of a medusome-person, and not to those portions which were 

 originally only organs of such a person. If this be so, it is necessary to assume in many 

 cases a far-reaching dislocation and multiplication of the parts which were originally 

 organs of a medusome. This assumption is directly supported by the fact that the 

 replacement of primary organs by equivalent secondary structures does to a very large 

 extent take place. As such vicarious organs {reserve or replacement organs, " Ersatz- 

 organe"), I interpret, for instance, the numerous swimming-bells and covering bracts 

 of many Physonectse, the successive heteromorphic swimming-bells of the Calyconectae, 

 the groups of palpons in many PhysoDectae. On the other hand, in such an instance 

 as the clustered groups of reproductive members, each separate " gonophore " is to be 

 interpreted as a medusoid person which has lost mouth-opening and tentacles. The 

 morphology and " sociology " of the Siphonophorae must take much more account than 

 heretofore of these important tectological distinctions, and the rank of individuality must 

 be more strictly defined. 



MONOGASTRIC and POLYGASTRIC CORMIDIA. 



The ordinate cormidia contain usually only a single siphon, more rarely two or more. 

 The most important forms of monogastric cormidia (with a single siphon) are the 

 following : — 



1. The Eudoxome of the Calyconectae (often becoming free as a " Eudoxia "), in 

 which each cormidium consists of two persons, one sterile (siphon with tentacle and 

 covering bract) and one fertile — the gonophore (often with accessory gonophores). 



2. The Ersseome of the Calyconectae (often becoming free as an " Erssea "), in which 

 each cormidium consists of three persons, having a medusoid " special swimming-bell " 

 added to the two persons above mentioned in the eudoxome. 



3. The Rhodalome of some Rhodalidse, of Hippopodius, Vogtia, Aurophysa, Canno- 



