EEPOET ON THE SIPHONOPHORvE. 7 



polygastric Siphonanthse the corniidia are lateral, originally metameric branches of a 

 segmented trunk or jointed stem. This appears, however, in very varied form, as the 

 cormidia occur in distinct order or irregularly scattered and dissolved. 



ORDINATE CORMIDIA. 



In most polygastric Siphonanths (and therefore in the great majority of now existing 

 genera of Siphonophora3) the cormidia are ordinate, that is, regularly arranged as the 

 metameres of the jointed stem or corm axis ; the intern odes, or regular intervals of the 

 stem between each tw r o cormidia, are often quite free, especially in much elongated corms, 

 as for instance in almost all polygastric Calyconectae, in a number of the Physonectse 

 (Apolemidse, many Agalraidae) and of the Cystonectae (Salacidse, many Rhizophysidae). 

 Not unfrequently in these stocks the elongated stem is so strikingly jointed by the 

 annular strictures separating the internodes at equal intervals, that the uniform and all- 

 pervading metameric structure of the Articulata is quite equalled. This comparison is 

 the more permissible, since the apical portion of the stem (representing the head) is 

 distinguished by the higher morphological differentiation of its group of persons. The 

 poly-organ theory might conceive these regularly jointed forms as Siphonophorae 

 articulatas in contrast to the others or Siphonophorae inarticulate. But even when the 

 stem is much shortened and the cormidia so closely compressed that the internodes are 

 hardly distinguishable, the cormidia are often arranged with great regularity in a com- 

 pressed spiral row, as in the Discolabidas and Rhodalidse. In others, and often in nearly 

 related forms, the regular arrangement disappears, and gradually passes into the scattered 

 disposition of Cormidia dissoluta. 



DISSOLVED CORMIDIA. 



While in the majority of polygastric Siphonanths the corms are distinctly articulate, 

 and the cormidia are arranged in regular succession, this original arrangement is more 

 or less lost in one portion of this group, and in some entirely. The dissolution usually 

 begins in this way, that the siphons and gonophores belonging to one cormidium 

 separate ; the latter bud off directly from the stem, often regularly alternating with 

 the first, as in Polyphyes among the Calyconectaa, in Linophysa, Nectophysa, 

 Rhizophysa, among the Cystonectse, and in many Agalmidae among the Physonectse. In 

 consequence of further dissolution of the stem arrangement, the palpons and the bracts 

 also lose connection with the cormidia, and bud out directly from the stem, as in several 

 Agalmidse and Forskalidse. Finally the ordinate arrangement is quite lost, and the 

 entire stem exhibits hundreds or thousands of different appendages (siphons, palpons, 

 gonophores, bracts, &e.) in irregular grouping, so that it is impossible to distinguish 



