Sim I '.-UN — A Revision of the GorgoncUidac. 323 



also the majority of the secondaiy branches may be only feebly developed, 

 but one may give rise to a large number of tertiaries. Sometimes, for 

 no apparent reason, tertiaries may arise from tlie secondary branches ; 

 but in all cases these arise on the inner side and ascend vertically, thus 

 maintaining the specific type of branches (fig. 41). 



Main CciTials. — In every tertiary and secondary branch there arc two 

 large canals running from end to end; those correspond with the bare 

 portions of the coenenchynia, and are consequently in the plane of branching. 

 In dried specimens their position is usually denoted by a groove due to the 

 collapse of the canal walls. In young colonies and in the upper part of large 

 colonies these secondary canals unite with the canals in the primary Ijranch, 

 one on either side ; but towards the base of older colonies they do not all 

 unite ; but the last three to ten may run parallel in the primary branches, 

 and so pass into the main stem, where as many as twenty may be visible 

 (figs. 42 and 43). 



Distribution of polyps. — In no case do polyps occur on the main stem. 

 On the primary branches they are restricted to the outer aspect, i.e., the side 

 diametrically opposite the one from which the secondary branches arise. On 

 the secondary branches they are disposed on the two inner surfaces — i.e., the 

 surfaces in the plane of branching are bare (fig. 44). In the upper half of 

 the secondary branches, however, the polyps may encroach on the bare spaces, 

 and appear as if distributed all over the coenenchyma. 



Nature of the verrucae. — In the younger parts of the colony the verrucae 

 are low and dome-like ; but in the older portions they seem to become smaller, 

 and in the lowest parts may appear as pit-like depressions. 



rig. 1 shows the structure of an expanded polyp. 



Spicules. — The spicules of this species might be said to consist almost 

 entirely of double-clubs, or, at any rate, of double-clubs and double-spindles 

 (fio-. 45). It is possible to group these into several distmct types which mat/ 

 show an evolution-series. It is noteworthy, however, that all are practically 

 of the same length, so that it is improbable that they are different stages in 

 development. The following groups, with their measurements, length by 

 breadth, in millimetres, may be distinguished :— 



(a) JDouhle-cluhs with hemispherical ends and a narrow bare constriction 

 definitely marked oil': 0057 x 0-038; 0-053 x 0-053; 0-053 x 0-034. 



(6) Double-clubs with the " heads " much more open than in («), i.e., there 

 is a distinct whorl of warts on either side of the constriction, 

 and the "hub" is very warty: 0-057 x 0-038; 0-057 x 0-034; 

 0-057 X 0-031. 



