P O L Y Z A 



165 



surface by which the tube or case (tubarium) in which the 

 polypide is enclosed is secreted. 



Both Rhabdopleura and Cephalodiscus produce colonies 

 by budding; but the colonies of the former are large, 

 definite, and arborescent, whilst those of Cephalodiscus 

 are remarkable for the fact that the buds do not remain 

 long in organic continuity with their parent, but become 

 detached and nevertheless continue to be enclosed by the 

 same common envelope or secretion. The bud-formation 

 of Rhabdopleura recalls that of Paludicella in the fact that 

 it leads to the formation of continuous arboriform com- 

 munities. That of Cephalodiscus resembles the budding 

 of Loxosoma, since no two fully-formed individuals remain 



Fig. 7. — Bhabdopleura Normani, Allman (original drawinss, Lankester). A. 

 A single polypide removed from its tube and greatly magnified, a, mouth; 6, 

 anus ; c, polypide-stallc or gymnocaulus/tlie " contractile cord " of Sars ; rf, thft 

 prae-oral lobe (buccal shield or disic of Allman); e, intestine; /, thoracic 

 region of the polypide ; g, one of the ciliated tentacles. B. Lateral view to 

 show the form of the buccal shield and its pigment spot, gr, ciliated tentacle 

 (in outline); A, basalridgeof theright armof theiophophore. C. Lateral view 

 of a polypide. i, ciliated patch (Sars's organ) at the base of the lophophore-arm. 

 other letters as above. D. Part of a lophophore-ai-m, with soft tissues rubbed 

 off to show the cartilaginoid slteleton. o, epithelium and soft tissues still 

 adherent at the tip of a tentacle; &, skeleton of tentacle; c, skeleton of axis. 

 E. Portion of a colony of Rhabdopleura Noiinani, showing the branched tube- 

 like cases formed by the polypides. The black line within the tubes represents 

 the retracted polypides connected together by their common stalk, the pecto- 

 caulus. Magnified to three times the size of nature. 



in organic continuity. Both Bhabdopleura and Cephalo- 

 discus (like Phoronis) produce cases or investments in 

 which they dwell. These are free secretions of the organ- 

 ism, and are not, like the coenoecia of Eupolyzoa, cuticular 

 structures adherent to and part of the polypide's integu- 

 ment. The dwelling of Rhabdopleura is a branched 

 system of annulated tubes of a delicate membranous con- 

 sistency, each tube corresponding to a single polypide, the 

 rings of which it is built being successively produced at 

 the termination of the tube by the secreting activity of the 

 prse-oral disk (fig. 7, E). The polypides freely ascend and 

 descend in these tubes owing to the contractility of their 

 stalks. On the other hand the dwelling of Cephalodiscus 



is a gelatinous, irregularly branched, and fimbriated mass 

 (fig. 8), excavated bynumerous cavities which communicate 

 withtheexterior.' In these 

 cavities are found the nu- 

 merous detached small 

 colonies of Cephalodiscus 

 (fig. 9), or we should rather 

 say the isolated budding 

 polypides. The remaining 

 important feature in the 

 organization of the Ptero- 

 branchia, namely, the parts 

 connected with the forma- 

 tion of buds, are best un- 

 derstood by first examining 

 Cephalodiscus. The body 

 of Cephalodiscus is seen 

 (fig. 9) to be an oval sac ; 

 in this is suspended the 

 U-shaped alimentary canal, 

 and from the walls of its 

 cavity (ccelom) the ova and 

 the spermatozoa are de- 

 veloped. Projecting from 

 the ventral face of this 

 oval sac is a muscular cy- 

 lindrical stalk, into which 

 the viscera do not pass, 

 though the coelom is con- 

 tinaed into it (fig. 9, c). 

 This stalk is merely the 

 outdrawn termination of 



tlip hnr^Tr Tf ic aVinnf oo FiG. 8. — Dwelling of gelatinous consistence 



me DOay. it is about as ana b,.owncolJurfo?med by the polypides 



long as the whole of the of cephalodiscus dodecalophm, M'Intosh; 



T.onf nf fli^ nv..'.v^n1 n-^A i^ Hatural size (from an original drawing 



rest 01 ine animal, ana it Wndly supplied by Prof. M'Intosh,F.E.S.). 



is from its extremity that o.polypidewithinthejelly;p,cavityonce 



.111 T T /n occupied by polypides. 



the buds are produced (fig. 



9, a). Before the buds have attained half the size of their 

 parent they become detached, but continue to occupy some 

 portion of the common gelatinous dwelling. 



Fig. 9. — A polypide of C^halodiscus dodecaiophus removed from the gelatinous 

 house (from an original drawing by Prof. M'Intosh). No organic connexion 

 has been severed in thus isolating this polypide with its attached buds a, a. 

 The figure represents the furthest point to which colony-formation attains in 

 this form, a, buds growing fi-om the bas-i of the polypide-stalk ; &, the prse- 

 oral lobe (buccal shield or disk) ; c, the polypide-stalk; d, tlie ciliated tentacles 

 of the twelve lophophore arms (six pairs, each like the single pair of Rhab- 

 dopleura) inextricably matted and confused; e, anterior margin of the prse- 

 oral lobe ; /, posterior margin of the same. Magnified about fifty times linear- 

 Turning to Rhabdopleura, we find that each polypide 

 has a body of similar shape and character to that described 

 for Cephalodiscus, and a similar ventrally developed 

 " stalk " (fig. 7, A, c). But, inasmuch as the buds deve- 



