Simpson — A Revision of Ihc Gorgonellidae. 299 



(3) The thickness of the coeneucliynia in lliu main steiu is seldom as 



great as in the branches or twigs, and is usually from 0"75 to 0'5 



times its thickness. 



Bearing these facts in mind, let us see if any inference may be made as 



to the mode of growth, and also as to the possibility of these apparently 



diverse forms being referable to a single species. 



(1) We find that what obtains with regard to the various measurements 



in different parts of the same colony also holds good in the 

 corresponding parts of colonies of different sizes. 



(2) It is also obvious that increase in thickness in the older parts of a 



colony is due, not to increase of thickness in the coenenchyma, 

 but to increase in the diameter of the axis. 



(3) Increase in length in the younger branches and twigs is not propor- 



tional to increase in the thickness of the coenenchyma, but tends 

 rather to the reverse of this situation. 



We are therefore in a position to conclude that increase in the thickness 

 of the coenenchyma is not proportionate to the age of the colony, but that 

 the coenenchyma attains to its typical tliickness at a very early stage, and 

 that further elongation and consequent thickness are caused more by the 

 growth of the axis than the coenenchyma ; or, in other words, the earlier 

 period of growth consists chiefly in development of the coenenchyma, while 

 the strengthening of the axis and elongation of the colony come at a later 

 period. Consequently the younger colonies are more bushy and fleshy, and 

 the older colonies have proportionately a greater amount of axis, and are 

 therefore more rigid. 



The distribution of the polyps, the nature of the verrucae, and the 

 details of the canal-system are exactly similar to those described for the 

 protruding verrucae variety of JmiccUa juncca. Figs. 18 and 19 have been 

 added to show the leading characteristics; and these should be compared 

 with the corresponding figures (12 and 13) of J. juncca. 



Colour. — The great majority of the specimens examined in this species 

 are of a dark brick-red colour ; l^ut the following tints also occur : — 

 (1) reddish orange, (2) brownish yellow, (3) orange-yellow, (4) lemon, and 

 (•5) creamy-white. There is thus almost a series of gradations from white 

 through orange to red. 



Spicides of J. gemmacca. 



The spicules of this species, as has already been pointed out, are identical 

 both in types and measurements with those oi J. Juncca, so that the description 

 and measurements given for the latter may be taken as typical. 



