78 Proceedings of the Boyal Physical Society. 



whole length of the sponge, and are placed at a distance of 

 about three millimetres apart, but of course this varies with 

 growth. 



The longitudinal fibres, which are external to the trans- 

 verse, are also compound. In the apical portion of the sponge 

 they are arranged at intervals of about three millimetres. 

 They enter largely into the formation of the coronal plate, 

 and sometimes bifurcate, so that a band which is simple 

 throughout the greater part of its length, is continuous with 

 two peripheral trabeculse of the plate. Towards the lower 

 extremity each band is resolved into its constituent fibrillse, 

 the basal prolongations of which form the root of the sponge. 

 These terminal fibres are barbed along their margins and at 

 their extremities. 



The transverse and longitudinal bands are bound together 

 by oblique fibres. These are not arranged in bundles, but 

 consist of a delicate network of primitive fibrilke, which pro- 

 ject into the large quadrangular spaces left between the two 

 former sets, reducing them to small rounded or irregular 

 openings. From the sides of the cylinder some of the fibrils 

 are produced outwards, forming the lateral ridges characteristic 

 of this species. The ridges are arranged in a number of 

 interrupted spirals. They are most marked towards the 

 upper extremity. 



The upper opening of the cylinder is provided with a coro- 

 nal plate formed by a number of stout anastomosing fibres, 

 which leave very irregular interspaces. The fibrillar enter- 

 ing into its composition are very intimately united, and the 

 coronal fibres have a dull, opaque, fused appearance, very 

 different from those of the parietes. This plate is convex 

 outwardly. At its periphery the parietal fibres are produced 

 upwards into a delicate frill, about four millimetres in height. 

 In this process the transverse and longitudinal bands are not 

 present. It consists entirely of very delicate reticular fibrils. 



From the consideration of the normal form of Euplectella 

 aspergillum we shall now turn to that of the abnormal 

 specimen which forms the subject of this paper, and we shall 

 find that its peculiarities relate entirely to the contour of the 

 sponge, not to its general structure or the arrangement of its 



