78 CALYCOSILVA CANTHARELLUS. 



only with a few small spines close to the end, follows the spiny region. This 

 distal part of the ray is conic and tapers gradually to a rounded end, 5-17 ii 

 thick. This has been observed only rarely in the hexactines of C. c. var. megony- 

 chia. One of the rays is thickened at the end, the terminal tyle attaining a trans- 

 verse diameter of 35 m- 



In some hexactines the rays are nearly equal in length. In most an often 

 very considerable difference in length of the individual rays is to be noticed. This 

 irregularity is usually due to one ray (Plate 1, figs. 16, 17, 22) or two rays 

 (Plate 1, figs. 14, 15) being more or less reduced in length. In the slender-rayed 

 hexactines, which are probably young forms, the rays thus shortened are similar 

 to the long ones. In the stout-rayed hexactines, which are certainly full-grown 

 forms, this difference in ray-length is associated with and obviously correlated 

 to a difference in the arrangement and shape of the spines, which renders the 

 appearance of the shortened rays often very different from that of the long ones. 



The spines of the spiny regions of the long, not reduced, hexactine rays 

 (Plate 1, figs. 14-18; Plate 2, figs. 4, 6, 11, 16) are conic, not very sharp-pointed, 

 and 5-35 ju long. They arise quite or nearly vertically and are not very close 

 together, on an average about 50 m apart. In some cases they seemed to bs 

 arranged spirally, but I could not verify this and was indeed unable to prove the 

 existence of any kind of regularity in their arrangement. The spines of the short, 

 reduced, hexactine rays (Plate 1, figs. 14, 15, 16; Plate 2, figs. 2, 14) are much 

 closer together, often in contact with each other at the base, and occasionally 

 branched. The branched spines (Plate 2, figs. 2, 14) consist of cylindroconic 

 stems, the ends of which are split up into from two to four stout, conic, obliquely 

 diverging, secondary spines. These spines somewhat resemble the protruding 

 rays of the sterrasters of the Geodidae. 



The silicoblasts building the rays of the hexactines possess, when they start 

 work, a certain amount of potential energy, E. This is expended in building the 

 ray and in forming the spines. The production of the former requires the work 

 Wi, the production of the spines the work W2. When their task is done the whole 

 of E will have been converted into work, W, and this W will be equal to Wi + W). 

 Under normal conditions there is a certain proportion between Wi and W2. 

 When, however, a spicule or some other obstacle prevents the silicoblasts from 

 producing a ray of the normal size, less than the usual proportion of W is ex- 

 pended on Wi so that, W being = Wi + W2, more remains for W2. This leads 

 to the hyperdevelopment of the spines actually observed on the shortened rays. 



The ray being much shorter and the spines more numerous and on the whole 



