RAPHYBTJS. 63 



which two other kinds of spicules, not noticed by these authors, must be 

 ViMed.— Surface Skeleton. The surface o£ tlie hard projecting ridges in the 

 surface-net is occupied by a number of small spicules, which form a layer 

 about 0-06 millim. thick ; these spicules are very variable in their shape, 

 straight or curved, with large and irregular spines all over the surface, and 

 particularly at the ends— spirastrellid ; they are of very uniform size, 

 and measure 0-03 millim. in length and 0-007 millim. in thickness. Besides 

 forming a dense armour on the projecting ridges, they are found scattered also 

 in the concave membranes of the me&hes.— Skeleton of the Hard Fibres. The 

 main support of the whole sponge is constituted by a reticulate mass of styli 

 and tylostyli, which are mostly situated longitudinally and disposed in such 

 a manner as to point towards the free surface in the projecting ridges, or 

 towards the soft pulpa in the meshes of the interior. These spicules are not 

 cemented together by any horny substance ; they are very abundant, and 

 form hard, dense masses throughout the fibres in the interior ; scattered, 

 these spicules are also but rarely found in the soft pulpa of the meshes in the 

 interior ; they are of uniform size, 0-5 millim. long and 0-02 millim. thick, 

 cylindrical, and abruptly pointed. The bulb of the majority of spicules 

 measures 0-03 millim. in diameter, sometimes it increases to a diameter of 

 0-036 millim., and may show indications of points at its greatest diameter; 

 one of these points may grow out to form a spine 0-09 millim. long ; this, 

 however, is rare. On the other hand the bulb may be absent altogether. 

 Proper styli are not nnheqnent.— Skeleton of the Pidpa. The soft tissue in the 

 meshes contains, besides scattered spicules of both the preceding kinds, also 

 small clusters of very slender and gracefully curved spined oxea; the clusters 

 of these are found scattered irregularly throughout the soft tissue and com- 

 prise from 7 to 12 spicules, crossing each other in a perfectly irregular manner. 

 These spicules attain a length of 0-2 millim. and a thickness of 0-003 milUm. ; 

 they bear short and sharp spines. 



in the soft tissue of the internal meshes remarkable granular, highly 

 colourable cells are met with in great abundance. The shape of these 

 elements in Raphyms hixonii is subject to great variations : the cells 

 are spherical, about 90 per cent, of them ; irregular lobose, 2 per cent. ; 

 spindle-shaped, 6 per cent. ; or with indications of dividing, 2 per cent. 

 A nucleus is indicated by a more transparent patch in the centre, but 

 it is not clearly visible. In stained specimens the whole cell (or, rather, 

 the granules) take up so much colouring-matter that the whole structure 

 is rendered non-transparent ; the nucleus in the fresh state and in spirit- 

 specimens is light and transparent because it is free from granules. The 

 granules are large, and refract the light very strongly. The differences in 

 shape between these cells lead me to assume that they are a peculiar kind 

 of amoeboid wandering cell. I further assume that in this case, as also in 



