Sponge-fauna of Norway. 141 



reous sponges. That an analogy exists is indubitable; but 

 the sphincters of Geodia and the like are not transitory, any 

 more than those of the ostia of some sponges, and they are 

 besides composed of far more highly specialized muscle-fibres, 

 arranged in a much more complex layer than is the case with 

 the fusiform contractile cells which serve to close the dermal 

 pores or ostia of any sponge which I have examined. 



The following table gives the equivalent terms used by 

 different authors, in four columns : the first gives the termi- 

 nology of Bowerbank, 0. Schmidt, and others ; the second 

 that of Carter and partly of Johnston ; the third of Hackel ; 

 and the fourth that adopted here. 



3. 4. 



Ilautporen. Pores. 



c , j , I Cortical funnel 



our-glass cavity, bubdermal cavity. < /■ c } 101ie j 



3. The Trichites. — These spicules form a layer which is 

 completely homologous with the layer of globates in Geodia 

 and the like ; and we may regard the trichite sheaf itself 

 as homologous with the globate spicule : in the one the 

 trichites have a radiate arrangement, and are fused together 

 in a round ball ; in the other they remain separate from each 

 other and, lying parallel one with another, form a cylindrical 

 bundle. 



Certain structural differences distinguish the trichite-layer 

 from the globate, independently of differences in the spicular 

 elements themselves ; thus in the Geodia-type of rind the 

 globules are united by ligaments of fine sarcodic (muscular ?) 

 filaments, while in our IStelletta the trichite sheaves are not 

 connected with each other by any intermediate tissue, but 

 simply lie loose in " pockets " of their layer. In both the 

 globate and trichite layers, however, certain spherical cells 

 lie amidst the spicules ; in the trichite layer these cells are 

 very similar to colourless blood-corpuscles, and possess a 

 nucleus with a round nucleolus ; the corresponding cells in 

 the globate layer are of a somewhat different character, as 

 will be noticed in our description of the Geodia rind. 



In examining sections of the trichite layer one constantly 

 meets with examples like that shown in PI. VI. fig. 16, where 

 the trichites remaining conjoined at one end have separated 

 and diverged at the other, and, dividing the sarcode of this 

 end between them, appear capitate with minute bead-like 

 particles of it. 



