CONTRIBUTION TO KNOWLEDGE OF KHABDOPLEtTRA. 635 



and finally embedded in it. This is best seen in the transverse 

 sections (PI. XLT, figs. 9, 10, 11, d, e,f). 



The gradual transformation of the soft stalk into the hard 

 stalk by the development of a chitiuous cuticle on its surface 

 can be readily traced in every growing branch of a Rhabdo- 

 pleura colony, and is seen in PL XXXIX, fig. 1, at the points 

 marked /, m, n. The hard stalk is '' the blastophore " or 

 " chitinous rod " of Allman, from which Rhabdopleura derives 

 its name. It does not appear from the writings of either 

 Allman or Sars that they had ascertained the nature of this 

 structure and its mode of formation. I should jfrefer to 

 employ for it a name which expresses the fact that it is only the 

 stalk of the leading polypide (for the time being) cuticularised 

 and fixed to the wall of the tubarium, and accordingly whilst the 

 contractile polypide-stalks are termed "soft-stalk^' or "gymno- 

 caulus," I would call the hardened portion '' pectocaulus," and 

 its cuticular investment the "stalk-pipe" or "caulotheca." The 

 pectocaulus is no less living than the gymnocaulus; although 

 no longer contractile the tissues within the stalk-pipe are in a 

 living state, and serve as a vital connection between the dif- 

 ferent polypides. The fact that the pectocaulus is a hard pipe 

 containing a soft medulla was established by Allman and con- 

 firmed by Sars. 



A very interesting fact comes to light when the true nature 

 of the pectocaulus is recognised, and this is that the chitinous 

 stalk-pipe or caulotheca is the true homologue — the morpho- 

 logical equivalent — of the coenoecium of an ordinary Polyzoon 

 colony. This equivalence makes it all the more necessary to 

 distinguish the tubular dwelling of Rhabdopleura by some 

 other name, and justifies the special term " tubarium." The 

 tubarium has no equivalent in Phylactolaemous and Gymno- 

 Isemous Polyzoa; the stalk-pipe or caulotheca is the coenoecium 

 of Rhabdopleura. 



An examination of figs. 1 and 3 in PI. XXXIX will now 

 render the chief facts as to the bud-formation in a Rhab- 

 dopleura colony, and the building up of the tubarium and its 

 transverse septa, intelligible. A branch of such a colony may 



