476 Prof. Reid on the Vogmarus Islandicus. 



extend through the whole height of the tubes, and the light is 

 transmitted freely through the transverse, and imperfectly along 

 the lines occupied by the vertical walls. This remarkable texture 

 enters very largely into the formation of the skeleton, being found 

 not only in the bodies of the vertebra but also in the inferior and 

 superior spinous processes, in the lower and middle parts of the 

 interneural spines, and in much the greater number of the bones of 

 the head. It is also present in the dermo-skeleton, for excluding 

 those bones of the head which some regard as forming a part of 

 the dermo-skeleton, it is found in the lateral line of the body. 

 This texture is chiefly arranged in the form of bands or plates 

 and tubes ; and in the series of little elevations placed on the 

 lateral line of the body it forms masses, from which branches pass 

 forwards and backwards along this line. The most frequent 

 form in which it presents itself is the tubular. I have stated 

 that this texture is very strong, and it requires considerable force 

 to break it up by the needles. It is composed of a hyaline tex- 

 ture, having, in some parts at least, some pale indistinct cor- 

 puscles scattered through it, so that though in some respects it 

 approaches the cartilaginous tissue, it could be very readily di- 

 stinguished from the true cartilage found in some other parts of 

 the body of the animal, chiefly from the absence of the nucleated 

 corpuscles or cells. One of the best methods of obtaining a good 

 view of this tissue in the vertebrse is to subject the parts contain- 

 ing it under examination to the action of aqua potassse, which 

 does not affect it, while it dissolves the surrounding texture. As 

 this structure depolarizes the light, when NicoFs polarizing 

 prisms are adapted to the microscope, the diff"erence between its 

 colour and that of the surrounding textures sometimes brings out 

 its arrangement very distinctly. The size of the tubes formed by 

 this tissue and the thickness of their walls varies. The walls of 

 some which I measured in the vertebrae were about yQ^^o^^ ^^ ^'^ 

 inch thick, and the calibre of the tube was about yyoth of an 

 inch in its longest and 2 jo*^ ^^ ^^ ii^ch in its shortest diameter. 

 The inferior spinous processes, and the lower parts of those su- 

 perior spinous processes I examined, seemed entirely composed of 

 this tissue arranged in the form of tubes similar to those in the 

 vertebrge, running parallel to each other, so that a longitudinal 

 section of them presented a number of parallel longitudinal lines 

 with spaces between them, while a transverse section exhibited a 

 reticulated appearance, produced by the open mouths of the cut 

 tubes. In the upper portion of the superior spinous processes, 

 and the greater portion of the interneural spines, it was chiefly 

 arranged in the form of one large tube, of a circular form gene- 

 rally, the interior of which was, in the spinous process, filled 

 up with a structure presenting all the appearance of cartilage 

 having numerous nucleated corpuscles (fig. 8), while in the inter- 



