58 THE VOYAGE OF H.M.S. CHALLENGER. 



connective tissue of many animals. They may be developed to strengthen the soft 

 ground-mass of the mesoderm, independently from the primary Keratose skeleton. The 

 fibrillar of the Hircinidse, ending at the two free ends with a club or knob, may be 

 regarded as monaxial Keratose spicules, similar to the siliceous " biclavated cylindrical 

 spicula" of Bowerbank. They strengthen the tissue of the Hircinidse in the same 

 manner as the elastic fibrillse in many kinds of connective tissue. 



The fibrillae of the Stannomidae seem to be more nearly related, physically as well as 

 chemically, to the common horny fibres of the Keratosa than to the similar filaments of 

 the Hircinidse. No single fact in their structure, arrangement, and development makes it 

 probable that they are independent organisms. Several botanists who have examined 

 them, and among them two fungologieal authorities, declared decisively that they are 

 neither fungi nor algse. I am therefore fully convinced that they are produced by the 

 sponge itself. 



Xenophya. — The solid foreign bodies which form the pseudo-skeleton and make up 

 the greatest portion of the body of the Stannomidse are either siliceous Radiolarian 

 shells, or calcareous Globigerina shells, or a combination of both materials. The pseudo- 

 skeleton is composed of pure Radiolarian ooze in five among the nine species, of pure 

 Globigerina ooze in two, and of a mixture of both in the other two species. The two 

 latter species {Stannophyllum pertusum and venosum) are most remarkable, since several 

 parts of the body (the strong ribs of the leaf) are mainly composed of the coarser 

 Globigerina ooze, whereas other parts (the intercostal plates) are composed of the finer 

 Radiolarian ooze. This fact, as well as others observed in the Psarnminidas and Spongelidae, 

 seem to uphold my opinion (stated in my description of the Physemaria) that these 

 animals possess a faculty of selection of materials in the construction of their pseudo- 

 skeleton. This opinion is supported, too, by Lendenfeld and Carter (1885), but it is 

 attacked by F. E. Schulze, Marshall, Polejaeff, and others. 



The xenophya are placed so densely and close together in all the Stannomidae that 

 the connecting maltha appears only as a scarce cement between them. They are never 

 enclosed in the spongin-fibrillae, but these run everywhere between the foreign enclosures, 

 either single or associated in bundles (PI. III. figs. 2-4, &c). When the dermal plate 

 of the sponge is well developed, the crossed bundles of fibrillse form subregular meshes, 

 in which groups of xenophya are placed, and the dermal pores are scattered at varying 

 distances (PL II. figs. 1-4, &c). 



Symbiontes. — Whilst the protecting sandy carapace of the Stannomidae is formed by 

 the agglutinated xenophya, the supporting scaffold, which gives stiffness and solidity to 

 the body when erect, is formed by a dense network of anastomosing chitinous tubes, filled 

 with a dark brown or blackish cellular mass. In the preliminary examination I supposed 

 that this constant network might be a constituent portion of the sponge itself, a tubular 

 skeleton similar to that of the Aplysinidse, composed of thin-walled heterogeneous fibres, 



