74 



THE VOYAGE OF H.M.S. CHALLENGER. 



dichotomously branched. The cylindrical branches are connected by numerous anasto- 

 moses and form a loose network, the meshes of which are 2 to 5 mm. in diameter. The 

 thickness of most of the branches is between 2 and 3 mm. The distal ends are 

 rounded or nearly truncate, sometimes club-shaped, not tapering or conical, as in the 

 preceding species. These differences, and especially the reticular shape of the sponge, 

 might perhaps justify its separation as a peculiar genus [Stannoplegma). 



Internal Structure. — Transverse and longitudinal sections through the branches of 

 the coralliform sponge exhibit the same structure as in the preceding species, viz. , a loose 

 framework of the symbiotic Hydroid (Spongoxenia), and between its meshes are the 

 branches of the canal-system of the sponge, and the skeleton composed of Kadiolarian 

 ooze and of spongin-flbrillge. The anatomical structure of the canal-system here also 

 could not be made out. 



Fibrillse. — The fine spongin-fibres are much more numerous, larger and more richly 

 developed, than in the preceding species ; they are arranged partly in bundles, partly 

 interwoven in all possible directions, in the cortical as well as in the medullary mass. 

 Most of the fibrillse are simple and run isolated, but often two to six parallel fibrillse are 

 found associated; more rarely there are small bundles of ten to twenty or more. Ramifi- 

 cations of the fibrillse, which I could not find in Stannoma dendroides, are not rare in 

 Stannoma corcdloides. The diameter of the larger fibres is 0*005 to 0*01 mm., that of the 

 smaller fibres O'OOl to 0"004 mm., often less. The firmer consistence of this species is 

 mainly produced by the richer development of the fibrillse, which surround and connect 

 the xenophya, or the foreign bodies composing the main mass of the sponge ; these 

 are, as in the preceding species, almost exclusively Radiolarian shells (figs. 2-4, r). 



Symbiontes. — The chitinous tubes of the symbiotic Hydroid are in this species less 

 numerous than in the preceding ; a transverse section of the branches exhibits usually 

 ten to fifteen tubes, rarely more, often less. The network of the tubes is in Stannoma 

 coralloides much looser than in Stannoma dendroides ; the Hydroid is apparently 

 Halisiphonia spongicola (PI. IV. fig. 9). 



