574 DR J. STUART THOMSON ON 



The polyps are enveloped at their bases by yellow calyces with numerous spicules. 

 These calyces are eight-partite above, but apparently the parts may become partially sub- 

 divided lower down. The polyps are completely retractile within the calyx. There is 

 remarkably little connection between the polyp proper and the calyx, and thus it is a 

 simple matter to slit open the calyx and remove the polyp. The polyp proper has no 

 spicules. The tentacles have about eight pairs of long narrow pinnules. The length of 

 the polyp after removal from the calyx is 3'0 mm., its greatest diameter 2'0 mm., the 

 diameter of spread of extended tentacles about 2'0 mm., the height of the calyx about 

 1*9 mm., the diameter of the calyx about 2*0 mm. The polyps are separated from one 

 another by a distance of about 2 mm. 



Transverse sections show that the stomodseal wall is fairly thick, the siphonoglyphe 

 is ciliated, and the muscles and mesenterial filaments are pretty well developed. 

 Transverse sections through the apical part of the coenenchyma show that the young 

 polyps situated in that region have only feebly developed muscles. It is also seen 

 that the ciliated groove is directed towards the rind or away from the centre of the 

 coenenchyma. 



The coenenchyma of the polyp-bearing part shows the following structure : — 



The rind contains numerous yellow spicules, which are double wheels of small size ; 

 in the central coenenchyma there are also double wheels, but these are comparatively 

 few in number. The canals of the external coenenchyma are larger than those of the 

 centre. In some parts, this reduction in the size of the central canals is very well 

 marked, producing greater compactness and some degree of solidity at the centre. 

 It may be that we have here a hint of a transition towards the formation of a 

 central axis. 



The stalk portions have a very irregular outline, partly due to the presence of 

 numerous spicules and partly to surface folds. The stalk portions show numerous 

 spicules (double wheels) in the rind, but comparatively few in the centre. The canals 

 of the stalks have a somewhat similar arrangement to that in the polyp-bearing part, 

 but the rind is much thicker ; the canals are smaller, and do not decrease in diameter 

 towards the centre. 



The spicules of all parts are double wheels. These double wheels are most abundant 

 in the calyx and more external parts of the colony, but they are also present in smaller 

 numbers towards the centre. Externally, the spicules lie very close to, and almost 

 protrude above, the surface. When a portion of the rind is treated with dilute eau de 

 Javelle and subsequently dried, a small portion of each wheel is seen to protrude above 

 the general surface of the ectoderm. The spicules from all parts may be termed double 

 wheels, but it will be noted from the following measurements that they are not quite 

 circular, the length being greater than the breadth in most cases. 



Dimensions : — 



(a) From the rind of the trunk, from 0-0432 by 0'0351 to 0'075 by 0*0621 mm., 

 and from 0'0486 by 0"0324 to 0-0729 by 0'0648 mm. 



