STRANDED AT LONGNIDDEY 215 



Transverse sections of the plates, examined with low magnifying powers, 

 were, however, the more instructive (fig. 20). The number and size of the 

 tubes was by no means uniform in the different parts of the same trans- 

 verse plane. Sometimes a single comparatively large tube was alone met with ; 

 at others two, or even a larger number, occupied the antero-posterior diameter, 

 and in this case the tubes were considerably smaller. The soft brownish- 

 yellow contents were readily recognised, and in many of the sections this sub- 

 stance was seen to be perforated with holes, which looked like transversely- 

 divided small blood-vessels. 



The solid portion of the plate was spotted with black pigment, and dis- 

 tinctly striated. The striae ran in two different directions, and indicated a 

 laminated arrangement. One set of striae or lamellae surrounded, in a concentric 

 manner, the individual tubes, and in their arrangement might be compared 

 with the lamellae surrounding the Haversian canals in a transverse section of 

 bone. They may be called the tubular lamellae ; and the tube, its contents, 

 and the lamellae surrounding it, might be termed a tubular system. The other 

 lamellae were situated on the peripheral part of the plate, and formed a sort of 

 envelope enclosing the tubular system of lamellae. These may be called the 

 peripheral or cortical lamellae ; and they formed that part of the plate which has 

 been called the cortical layer or " enamel" of the whalebone. When examined 

 with higher powers of the microscope, the lamellae were seen to be composed of 

 elongated and flattened cells, each containing a distinct nucleus, and more or 

 less black pigment (fig. 21). These cells were obviously peculiarly modified 

 epithelial cells. The intervals between the outermost lamellae of adjacent 

 tubular systems were filled up by cells, which presented less of a flattened and 

 more of a fusiform or rod shape ; these cells, though interstitial in their position, 

 were apparently continuous with the cells of the cortical layer. 



Transverse sections through the setae displayed in each a central tube or canal, 

 surrounded by the usual arrangement of concentric tubular lamellae (fig. 22). 

 The tube within the seta contained a similar soft brownish material to that 

 found in the tubes within the blade itself. Each seta represented, therefore, 

 a single tubular system. 



When vertical sections through the intermediate substance, in which the 

 bases of the plates were imbedded, were examined with low powers of the 

 microscope, the deep surface attached to the palate was seen to be much more 

 highly charged with pigment than the more superficial parts, and so regularly 

 was it disposed, that it might almost be described as a special pigmentary 

 layer of the structure. The deep surface had an uniform rich black colour, and 

 was perforated by numerous apertures, which in the vertical sections were seen 

 to lead into clefts which passed some distance into the intermediate substance 

 (fig. 23). The black pigmentary layer was prolonged along the walls of these 



