356 SYDNEY J. HICKSON. 



— extend from the surface right down to the base ; but others 

 — the secondary polyps, which are formed during the later 

 stages of growth as buds from endodermic canals proceeding 

 from the coelentera of the primary polyps — terminate at various 

 depths in the substance of the colony, according to the stage 

 of growth at which they were formed. 



My first impression on examining the anatomy of the colony 

 was that the coelentera of the secondary polyps fused directly 

 with those of the primaries, but I am now convinced that this 

 impression was an erroneous one. The secondary polyps 

 terminate in the mesogloea, but as the terminal end is usually 

 connected with neighbouring coelentera by short open canals, 

 they cannot be said to terminate blindly (PI. 37, fig. 8). 



When a thoroughly contracted specimen of Alcyonium is 

 examined the surface may be seen to be covered with a number 

 of rounded prominences, each bearing in its centre a star- 

 shaped depression. These prominences indicate the position 

 of the polyps, and are on an average 1"5 mm. in diameter. 

 In a few instances I have measured prominences as much as 

 2 mm. in diameter, and several young buds are very much 

 smaller than the average dimensions given above. 



On the upper free parts of the colony the polyps are very 

 closely packed, so that in the contracted condition there is 

 very little space between the protuberances ; but on the sides 

 near the base of the colony the protuberances are frequently 

 separated by considerable intervals. In a specimen I obtained 

 some years ago oflf the coast of North Wales the base of the 

 colony is spread out like a membrane over a Serpula tube, 

 and in the outer portions, where the base is thinnest, the polyp 

 protuberances are as much as 1 — 3 mm. distant from one 

 another. 



In a fully expanded colony the base of the extensible portion 

 of each polyp averages 2 mm. in diameter, but it is not so easy 

 to give the exact length from the mouth to the surface of the 

 colony, on account of the extreme sensibility of the polyps 

 during life. 



It is quite probable that in the fully expanded condition, in 



