390 Mr. T. H. Stewart on the young state of Ophiocoma rosula. 



are placed at regular distances^ and the spine becomes symme- 

 trical, and assumes that beautiful form depicted in fig. 8; 

 and figured by Prof. E. Forbes, who says, " the lightness and 

 beauty of which might serve as a model for the spire of a 

 cathedral.^' 



The most interesting of all these spines are the third set, or 

 hooked ones, which occupy the tip and a portion of the under 

 surface of the extremities of the rays. They are not unlike 

 reaping-hooks, only they have a secondary hook below, just at 

 the point of the junction of the handle and blade. They 

 also have a tubercle below this on the handle, but this is never 

 formed into a decided hook like the other two above. It 

 was the existence of these hooked spines that led me to fancy 

 the young O. rosula a new Ophiocoma. But in order to be quite 

 sure on the subject, and not to make new species without careful 

 investigation, I boiled some older O. rosula in caustic potash ; 

 and on examining the result, I found the same hooked spines to 

 be present. 



By examining and comparing the spines of these young with 

 those of an adult O. rosula, it will be noticed that the hooked 

 ones do not grow in the same proportion as the rest ; for in the 

 adult, though they still keep the same form, they are very small 

 in comparison to the other spines, whereas in the young they 

 are of the same size and serve an important office, viz. enabling 

 these young and feeble starfish to gain a firmer hold of the sub- 

 stance on which they crawl, so that they are not drifted ofi" by 

 every slight force to which they are exposed ; and indeed I found 

 that while they were alive it required a considerable efi'ort to 

 separate them from their attachment. 



It would appear therefore that these hooks are specially pro- 

 vided for the young condition of the starfish, and is another 

 beautiful instance how Nature modifies parts of the body to 

 meet the special requirements of animals under varying circum- 

 stances. These hooked spines have the same rounded base and 

 constriction as the others, and they then form the sickle-like 

 termination. 



Parallel with this terminal hook in about the middle of the 

 spine another is formed, which is not so long or large as the 

 terminal one ; and at an equal distance below this second hook 

 is a little tubercle, which is not developed into a hook, but is 

 perforated with small holes, as also is the base, giving it when 

 only slightly magnified a granular appearance. 



I have never found more than two hooks on a single spine, 

 except in one adult animal, where on one of the spines there 

 were three; but the lowest near the base was very rudimentary. 



All the spines are covered with the animal membrane before 



