REPORT ON PHORONIS BUSKII. 9 



the support of the softer tissues of the body, and especially for maintaining the shape 

 of the vascular spaces anteriorly, and protecting the nervous masses. Its various 

 concentrations as well as its delicate expansions are admirably adapted for the functions 

 of the parts, and it is apparently of considerable elasticity. By its greater development 

 it affords a contrast with the condition in RJiahdojjleiira and Cephalodiscus, as well 

 as with Loxosoma and other members of the Entoprocta. It has not hitherto, perhaps, 

 received that attention which it merits ; indeed some, including Mr. Caldwell, refer to 

 it only incidentally in connection with other parts as the homogeneous basement 

 " membrane." 



Muscular System. — Anteriorly the main concentrations of the muscular system 

 take place in the centre of the whorls (PL III. figs. 1 and 2), the fibres radiating 

 outward from the skeletogenous axial support, and thus readily controlling the volu- 

 tions of the branchial fans. In longitudinal sections these muscles often present a 

 scalariform appearance (PL III. fig. 1), being ranged in somewhat regular series one 

 above another — each radiate series to its own branchial whorl. At the base of the 

 latter, that is, when both branchial fans have amalgamated, the radiate muscles still 

 occupy the centre, having at each side internally {i.e. towards the median line) the 

 skeletogenous tissue, and externally the vascular space. 



As soon as the body-wall is distinctly formed, a layer of circular muscular fibres 

 {cm) is found within the basement-tissue, and these fibres subsec[uently attain greater 

 development. In the region just mentioned, the radiate fibres, which pass from the 

 body-wall between the pennate portions of the next coat to the alimentary canal, 

 apparently perform the main contractile functions. The circular fibres continue to the 

 posterior end, and aid, by amalgamation with others, in closing the body-wall there. 



The next or longitudinal coat {Ipm) is anteriorly {i.e. immediately behind the 

 tentacles) rather irregularly arranged, being grouped as somewhat massive fasciculi, with 

 or without intervening radiate fibres from the basement-tissue, or assuming the form 

 of isolated bands — the precursors of the pennate fasciculi. As soon as the body-wall 

 has a median neural ridge and two lateral, the longitudinal muscular layer forms a series 

 of elongate and somewhat pennate fasciculi in transverse section (PL I. fig. 4), many 

 being separated by the radiate fibres especially along the ventral curve. The inter- 

 mediate radiate bands are often of considerable strength, and pass from the circular 

 coat inward to the wall of the alimentary canal, and it is the arrangement of these that 

 gives the somewhat sinuous outline to the ventral curve. A very strong band {rm) 

 occurs on each side of the intestinal mesentery, and thus prominence is given to the inter- 

 mediate region of the body- wall ; and a similar disposition of the parts causes the lateral 

 elevation on each side, that on the right containing a large vascular trunk. Proceeding 

 backwards, the pennse become less elongate in transverse section, the somewhat con- 

 stricted external region or base presenting a pair of large fibres, while the ovate leaf-like 



(ZOOL. CHALL. EXP. — PART LXXV. 1888.) Ffff 2 



