BY E. F. HALLMAXX. 513 



diffitation, which reticulate amonjjr themselves to form a narrow- 

 meshed network between the main fibres {of. PI. xxxii., figs. 

 3, 4, 5). The first-mentioned, or radially directed fibres appear 

 usually to arise by the branching of one or a few axially situated 

 fibres running lengthwise : but, in some instances, no such 

 primary main fibres are observable, the radially-directed fibres 

 each arising independently. In addition to the paucity or 

 absence of longitudinal main fibres, the skeleton also presents 

 two other characteristic and distinctive features : the radial 

 fibres are arranged for the most part in a more or less ortho- 

 stichous manner, and, almost without exception, the connecting 

 fibres between them occur only between those belonging to the 

 same orthostichies. Hence it follows that the connecting fibres 

 are confined almost exclusively to vertical (or, as one might almost 

 sav, to meridional) planes; and thus, in a transverse section 

 of a digitation (PI. xxxii., fig.2), the main fibres appear to be 

 without connections. The pattern of the reticulation formed by 

 the connecting fibres is also characteristic, the meshes usually 

 being elongated and narrow, with their long axis in the direction 

 perpendicular to the main fibres. The main fibres vary in stout- 

 ness from 120 to 350/a; tlie spicules composing them are fairly 

 closely and regularly packed, seldom slightly plumose in their 

 arrangement, and are cemented by a relatively small amount of 

 spongin, seldom sufiicient in quantity to form a distinct sheath. 

 The connecting fibres are peculiar in being thin and ribbon- 

 shaped, and are mostly paucispicular and composed chiefly of 

 spongin. Echinating spicules occur similarly as in A . pficafa; but 

 they are here very rare upon the connecting fibres, and are scarce 

 even upon the main fibres. Interstitially scattered megascleres 

 are relatively very few. The microscleres have the same distri- 

 bution, and are equally as abundant as in A. plicata. 



In the massive body of the sponge, as already stated, the 

 skeleton consists of interunited components each constructed on 

 the same plan as the above-described skeleton of a single digita- 

 tion. The interconnection between the components is effected 

 simply by the prolongation of the radial (main) fibres of one 

 component, and their ultimate union with connecting fibres of 



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