580 THE MICROSCOPE. 



one of the long bones, and contrasted with that of a 

 mammal or bird, we shall notice at once the difference 

 which the reptile presents: there are very few, if any, 

 Haversian canals, and these of large size ; and at one view, 

 in the section, Fig. 317, we shall find the canals and the 

 bone-cells arranged both vertically and longitudinally : the 

 bone-cells are most remarkable for the great size to 

 which they attain; in the Turtle they are 1-3 75th of 

 an inch in length, the canaliculi are extremely numerous, 

 and are of a size proportionate to that of the bone-cell. 



" In fishes we have a greater variation in the minute 

 structure of the skeleton than in either of the three classes 

 already noticed ; and there are certain remarkable pecu- 

 liarities in the bones of fishes which are so characteristic, 

 that a bone of one of these creatures can never be con- 

 founded with that of any animal of a higher order, when 

 once its true structure has been satisfactorily understood. 

 Of all the varieties of structure in the bones of fishes, by 

 far the greater number exhibit nothing more than a series 

 of ramifying tubes, like those of teeth j others exhibit 

 Haversian canals, with numerous fine tubes or canaliculi, 

 like ivory tubes, connected with them ; a few consist of 

 Haversian canals, with fine tubes and bone-cells, Fig. 319 ; 

 and a rare form, found only as yet in the sword of the 

 Swordfish (Istiophorus), exhibits Haversian canals and a 

 concentric laminated arrangement of the bone, but no bone- 

 cells. The Haversian canals, when they are present, are of 

 large size, and very numerous, and then the bone-cells are, 

 generally speaking, either absent or but few in number ; . 

 their place being occupied by tubes or canaliculi, which 

 are often of a very large size. The bone-cells are remark- 

 able for their graduate figure, and the canaliculi which 

 are derived from them are few in number; they are 

 seen to anastomose freely with the canaliculi given off 

 from neighbouring cells ; and if the specimen under ex- 

 amination is a thin layer of bone, such as the scale of 

 an osseous fish, from the cells lying nearly all in one plane, 

 the anastomoses of the canaliculi are seen beautifully 

 distinct. In the hard scales of many of the osseous 

 fishes, such as the Lepidosteus and Calicthys, and in the 

 spines of the Siluridce, the bone-cells are beautifully seen ; 



