Sponge-fauna of Norway. 401 



lar cells, which do not differ in general characters from 

 the isolated definite oval cells which have already been 

 mentioned as occurring here and there in the mark and sub- 

 cortical layer : many of them, indeed, are identical with these 

 in all respects ; but most differ in form, becoming much elon- 

 gated in the direction of the spicular bundle, and thus acqui- 

 ring a more or less fusiform outline. The nucleus is involved 

 in this change of form, becoming also elongated and fusiform; 

 but the nucleolus is unaffected and retains its spherical form. 



These fusiform cells, by becoming gradually hyaline, afford 

 an easy passage into (ii) ordinary hyaline fibres of precisely 

 the same nature as those of the subcortical layer ; they lie 

 parallel to the spicules of the spicular bundle, to which they 

 form an enclosure. Sometimes a surrounding band of con- 

 centric fibres occurs around the bundle. Finally, (iii) a small 

 quantity of gelatinous connective tissue is in places associated 

 with the spicular bundles. 



Where the spicular bundles enter the cortex the fusiform 

 hyaline fibres can be easily followed, diverging from the spi- 

 cules in a gentle outward curve and entering the subcortical 

 layer, which therefore may be regarded as an extension of the 

 tissue of the spicular tract, modified by increase of growth 

 and change of direction. The change of direction is in ac- 

 cordance with that of the long-shafted spicules, the trifid ends 

 or distal rays of which tend, on reaching the rind, to become 

 more concentric and less radiate in direction. Just below the 

 place where the fibre curves from the spicules to the cortex a 

 number of granular cells, like those described in the same 

 position in 8. Normani, are often found accumulated. 



In addition to a tissue of the bundle there is the tissue of 

 each individual spicule, each being invested in an excessively 

 thin structureless membrane containing small round nuclei 

 surrounded by fine granules and very thin structureless fibrils 

 (PI. XVII fig. 2, s). Now and then one finds isolated hyaline 

 fibres encircling a spicule like a girdle (PI. XVII. fig. 2, z) ; 

 the meaning of this feature, which is to be found in other 

 related sponges, is not apparent. 



Globates. — The structure and development of these spicules 

 can be studied with great facility in this sponge. The earliest 

 form consists of a cell (PI. XVII. fig. 21, s) oi* the same size as 

 the common, isolated, oval, granular cell of the mark (PI. XVII. 

 fig. 21, m) ; it contains the little sphere of radiate trichites, 

 which are united together at their inner ends about a small, 

 central, spherical space ; externally they terminate in a layer 

 of hyaline sarcode or cell- wall. On one side of the cell is 

 imbedded a round or, more commonly, oval nucleus with its 



