Mr. H. J. Carter on the Structure o/Tethya dactyloidea. 83 



" On making a vertical section of the sponge, the terminal 

 aperture is observed to divide into a number of branches, 

 which, subdividing, permeate the mass generally down to its 

 base. 



" Immediately where the aperture begins to be divided is a 

 portion of the fleshy substance which is more dense than the 

 rest, owing to the presence of a greater number of spicules 

 and their smaller size, from which also arises a framework 

 chiefly composed of acerate, slightly curved spicules of dif- 

 ferent lengths (fig. 4), that more or less, in bundles, extends 

 in a radiating manner backwards to the periphery of the body 

 generally. No spicules take the opposite direction, as in the 

 globular species [T. arabica^ see 'Annals* vol. iv. p. 1, July 

 1869), where this denser part, which represents the ' nucleus,' 

 is at the base or middle, and not at the summit of the species. 



" Throughout the fleshy mass, which is very tough and 

 elastic, are a number of little white specks, of different sizes, 

 which can be seen with a magnifying-glass of low power, 

 being about 4-4300ths of an inch in diameter. They are 

 spherical, filled with granules, and chiefly visible about the 

 middle of the body. With them, also, is occasionally seen a 

 much larger spherical one (viz. ll-4300ths of an inch in dia- 

 meter), which seems to have a hilous opening, and is covered 

 with points more or less quincuncially arranged. The former 

 are probably sponge-cells, and the latter the gemmules. 



" Where these bodies were most numerous there was also 

 an abundance of minute C- and S-shaped siliceous bodies 

 [bihamates], which in some places were not single, but in 

 groups, as if developed in cells. These average l-1800th of 

 an inch long in the curve " (fig. 5). 



Thus on the south-east coast of Arabia we have a sponge 

 very like Schmidt's TetiUa polyura (Atlantisch. Spong, Faun, 

 p. 66, tab. vi. f. 8), which came from Iceland, with only 

 these diflerences, viz. that in the latter the surface was not 

 uniform, but interrupted by nodular projections, and among 

 the in^equifurcf^te spicules there were also anchor-headed ones. 

 Of the colour Schmidt states nothing; and there are no 

 anchor-headed spicules represented on the surface of the body 

 in his figure, all being confined to the long bundles at the 

 base, where there is an equal absence of forked spicules (just 

 as in Tetliya dactyloidea), as if they had been intended to act 

 as little grapnels in the sand. But how fares this inference, 

 when, in Tethya casida {' Annals,' Aug. 1871, vol. viii. pi. 4), 

 there are no anchor-headed spicules in any part of the sponge, 

 and the long spicules which were imbedded in the sand, si- 

 milar to those of the foregoing species, are all forked ? Is it 



6* 



