332 SURGEON F. H. WELCH ON THE ANATOMY OF 



of the colony ; and it is at once apparent that there is a distinct 

 separation of the visceral space (/) from the encircling body- 

 constituents, the latter consisting of a cutaneous envelope and 

 parenchyma compounded of a soft albuminoid material, muscular 

 fibres, and inorganic nodules. The cutaneous envelope (fig. 3 a, 

 fig. 5 a) averages f-o'o o" i^<^^ ^ thickness, consisting of a thin 

 transparent chitinous layer externally, and a dark granular pro- 

 ductive layer beneath. The parenchyma extends from the skin 

 externally to the fibrous boundary of the visceral space internally, 

 and is arranged as follows :— rNext to the granular layer of the 

 skin is a circular layer of involuntary muscular fibre, which for 

 the space of y^rr ^^ch is free from all intercepting fibres (fig. 5, c), 

 but beyond that is intermingled with transverse muscular fibres, 

 forming a continuous layer for about yo1> ^'^'^^ (%• ^' ^)j after 

 which they are both thickly studded with "calcareous particles," 

 forming a well-defined layer of -^-^ inch thickness, and following 

 the contour of the body-surface (fig. 3, c ; fig. 4, c ; fig. 5, e). The 

 transverse fibres, although forming a continuous layer outside the 

 inorganic granule layer, yet on the inside of it are collected into 

 uniform thin bands, which form a meshwork enclosing the soft 

 albumenoid material and the longitudinal muscular bands of the 

 body (fig. 3, d ; fig. 6, a) ; and this meshwork is continued on to 

 the fibrous boundary of the visceral space. The longitudinal 

 muscular bundles (fig. 4, d) pass continuously, for the major part, 

 from one segment to the other throughout the colony. 



As regards the inorganic accretions (" calcareous particles") 

 (fig. 7), these are oval spherical or somewhat irregular in ovitline, 

 homogeneous, or made up of concentric laminae arranged around a 

 nucleus, pale yellow or brownish in colour ; average size — ~ 



' f .' 5 & 10 



inch. The major number are composed of lime carbonate, the 

 minor (generally irregular in outline) of phosphates or inspissated 

 fat compounds. The use and mode of arraugement in particles 

 of this inorganic layer is apparently, as I have elgewhere more 

 fully stated *, for the purpose of giving a firmness to the body- 

 structure while allowing at the same time of pliability and move- 

 ment of the one part upon the other. 



A distinct fibrous layer divides the body-parenchyma from the 

 visceral substance ; it is connected to the inner surface of the 

 cuticle at the lateral edges of the zooid (fig. 3, e), and is conti- 

 nued longitudinally from one segment to the other, passing up 



* Quarterly Microscopical Journal, Januai-y 1875, p. 6. 



