P L Y Z O A 



165 





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

 polypide is enclosed is secreted. 



Both llhabdopleura 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 Khabdopleura 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 



9 



FIG. 7. Rhabdopleura A'ormnni, Allman (original drawings, Lankcster). A. 

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

 anus ; c, polypide-stalk or gynraocauliu, the " contractile cord " of Sars ; rf, the 

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

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

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

 (in outline); A, basal ridge of the right arm of the lophophore. C. Lateral vic'w 

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

 Other letters as above. D. Part of a lophophore-arm. with soft tissues rubbed 

 off to show the cartilaginoid skeleton, a, epithelium and soft tissues still 

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

 E. Portion of a colony of Rhabckipleura Normani, 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 Khabdopleura 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 ccencecia 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 by numerous cavities which communicate 

 with the exterior. 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 ccelom is con- 

 tinued into it (fig. 9, c). 

 This stalk is merely the 

 outdrawn termination of 

 the body. 



long as the whole of the 

 rest of the animal, and it 

 is from its extremity that 

 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. 



It is about as FlG ' S. Dwelling of gelatinous consistence 

 and brown colour formed by the polypides 

 of Cephalodiscus dodecalophltt, M'lntosh; 

 natural size (from an original drawing 

 kindly supplied by Prof. Jl'Intosh, F.R.S.). 

 o, polypide within the jelly ; p, cavity once 

 occupied by polypides. 



FIG. 9. A polypide of C?i>hatv<U*cus (Jotffcaiopkus removed from the gelatinous 

 house (from an original drawing liy Prof. M'lntosh). No organic connexioq 

 has been severed in thus i^nhiling 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 from the bas ; of the polypide-stalk ; b, the prse- 

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

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

 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- 



