30 STRUCTURE AND GROWTH 



be viewed either as canaliculi which penetrate from the cell-cavity 

 into the thickened cell-walls, or as hollow prolongations of the 

 cells into the intercellular substance. In the first case, they 

 might be compared to the porous canals of vegetable cells ; in 

 the second, they would correspond with prolongations of 

 cells, such as we shall often again meet with in the progress of 

 this work. Meanwhile, for an example of those cells which 

 are extended out on all sides into canals, and which I have 

 called stellated cells, the reader is referred to plate II, figs. 8 

 and 9, where those transformations are delineated from pigment- 

 cells. I decidedly give the preference to the latter explanation 

 of the canaliculi, because they pass through the entire thick- 

 ness of the firm cartilaginous substance, a fact which, in order 

 to be consistent with the first view, requires for its explanation 

 that the substance between the cell-cavities should be formed 

 of the thickened cell-walls, which is certainly not the case 

 in the cartilages of mammalia, as is seen in plate III, fig. 2. 

 The osseous corpuscles, with their canaliculi, would therefore 

 be the cartilage- cells transformed into stellated cells, and filled 

 with earthy matter. We shall return to this metamorphosis 

 of round into stellated cells when treating of the pigment. The 

 resemblance between stellated pigment-cells and osseous cor- 

 puscles is sometimes very striking, as is shown, for example, 

 by the pigment-cell which lies to the extreme right in plate II, 

 fig. 9. The compact bony substance is intercellular substance ; 

 it is, however, probable that the walls of the stellated osseous 

 cells form some, if only a very small part, of it. 



When ossification takes place, the earthy matter is first de- 

 posited in this intercellular substance, and probably at a sub- 

 sequent period also in the cell-cavities. The deposition often 

 causes the substance to assume a darkish granulous appearance 

 in the first instance, which it afterwards loses, becoming more 

 equally dark. If we assume, what is extremely probable, that 

 the earthy matter is contained in bones in combination with 

 the cartilaginous substance, in a manner analogous to a che- 

 mical union, and not in the form of minutely-divided granules, 

 the mode in which the union with the earthy salts takes place 

 may then be explained in two ways : either the earthy matter 

 combines with a particle of cartilaginous substance in such a 

 manner that each smallest atom receives in the first instance a 



