294 Dr. J. E. Gray on the Spicules o/'Hyalonema. 



each of them and forms the mass of them, and that they are a 

 part of the community of the Palythoce^ and not a mere bmidle 

 of spicules arising out of the sponge. 



If I understand the theory of those who regard the rope-like 

 axis of Hyalonema as the spicules of a sponge, they believe 

 that the spicules of the sponge are clustered together in the 

 centre of the sponge, and are produced, forming an elongated 

 columnar coil, which, according to Bowerbank, is covered 

 with a skin forming part of the sponge, and according to 

 Professors Brandt and Max Schultze is covered with a coat 

 of parasitic Palythoce. If either of these theories is true, the 

 spicules should be of the same form and structure as the spi- 

 cules of sponges, and complete and acute at each end. 



I have shown that the spicules of the coil are not formed 

 as the usual spicules of Sponges, but have their ends, and 

 especially their upper or distal ends, always in an incomplete 

 state of development, and that they are constantly being 

 lengthened by the addition of coats to the end of each of the 

 layers of which the spicules are composed. I think we may 

 conclude that the spicules are produced or secreted by the coat 

 of corium that covers them (and this coat has, I think, been 

 most indisputably proved to be formed by the community of 

 animals allied to Palythoa), and therefore that the axis is not 

 a part of the sponge, but the proper secretion of the Palythoan 

 animals. 



Prof. Max Schultze, though he figm-es this structure (t. 2. 

 f. 4&5), appears not to understand its importance; for he 

 compares it to a fusiform spicule with a central spherical 

 knob that he found in the sponges which are furnished with 

 some spines which are directed towards the centre. But this 

 is evidently only a variety (and one I have not seen) of the 

 stellate spines figured on tab. 4. f. 2, 4, 7, 8 & 9, though in these 

 the spines on the rays are all directed towards the tips. These 

 spinulous spicules are all perfect and acute at the tips, and are 

 not truncated and growing at the end like the spicules of the 

 coil of Hyalonema. 



Prof. Brandt's figures of the spicules of Hyalonema^ on tab. 2. 

 f. 12, 13, 14, & 15, much more accurately represent the structure; 

 but it is to be remembered that figs. 12 & 13 represent wrong 

 ends of the spicule upwards ; that is to say, the slender end of 

 the spicule is the one that is immersed in the sponge, and the 

 blunt truncated lower end, as it appears in these plates, is the 

 end of the spicule that is furthest from the place of attachment 

 and which is being extended to accommodate itself to the in- 

 creased height of the bark or community of polypes. And 

 tab. 4. f. 14 also well represents the coat of which the spicules 



