266 



proper. Growth still takes place, and a zooid is the result, consisting of 

 a comparatively long stalk bearing the anthocodia. That this is the 

 mode of growth is clearly demonstrable in the younger colonies, and 

 also in the less advanced polyps round the periphery of the older colo- 

 nies. Fig. 4 represents a colony where this is the maximum development 

 attained, the zooids however being introverted. As the colonies grow in 

 size, the Verrucae also become more complicated, the terminate stellate 

 part expanding horizontally to form an octagonal disc, with the indenta- 

 tions less pronounced, containing eight cavities which correspond to those 

 formed by the retractor muscles. To complicate matters still further, 

 towards the centre of the older colonies, Verrucae which correspond to 

 the jjrimary canals fuse with the adjoining Verrucae so that the canals 

 are now continuous. 



Fig. 5 represents a surface view of one of those isolated octagonal 



Fig. 10. 



Fig. 8. 



Fig. 9. 



Fig. 8. Enlarged section through a wall showing the spicule cavities and the residue 



of the organic axis («) (X 12). 



Fig. 9. Zooid enlarged (x 8). 



Fig. 10. Vertical section through a verruca and stem canal with the zooid introverted 



(x8). a, outer wall of the verruca; ft, wall of the zooid stalk; e, zooid; d, i-etractor 



muscle of the zooid; e, mesenteries with ova. 



discs closed over the introverted zooid — the indentations correspond- 

 ing to the fused walls, and the raised portions indicating the position of 

 the canals, the spicules being arranged biserially along the eight radii. 

 A vertical section through a complete colony is given in fig. 6, while 

 fig. 7 shows the method of arrangement and growth as detailed for an 

 individual isolated polyp and stem canal, the zooid being in this case 

 everted. The partitions of the canals are densely spiculose, in addition 

 to the outer feltwork, and a cross section shows that the spicules are 

 arranged for the most part vertically, the cavities conforming to the 

 tubercules on the spicules (fig. 8). 



