A YORKSHIRE NATURALIST 127 



bones, where they gradually developed into ordinary 

 oral teeth of that class of fishes. 



These views, already adopted by Huxley and 

 Kolliker, were alike based upon my discoveries of 

 what took place in fishes' scales, and their recogni- 

 tion as the representation of teeth. 



Whilst pursuing the above investigation, and 

 especially keeping in view the question of the origin 

 of the lacunae of bone, I made the discovery that a 

 large number of fishes contained no lacunae, though 

 in others they were abundant. The same research 

 also brought prominently to light further facts. I 

 found that in many of the so-called cartilaginous 

 fishes i.e., sharks and rays only one kind of bone 

 exists, which is produced by deposit in the inter- 

 cellular spaces of the cartilage, of which all bones 

 primarily consist, and of a phosphate of lime, which 

 gives additional firmness to the skeleton. Bone thus 

 formed I designate chondriform bone. Amongst 

 the ordinary bones of fishes I discovered two forms 

 of bone an inner one of chondriform type growing 

 inwards, and an outer one deposited in the succes- 

 sively superadded layers of the periosteum, on the 

 membranous layer with which all mammalian bones 

 are invested. Successive layers of this membrane 

 were added to the pre-existing ones so long as the 

 period of the animal's growth continued, the pre- 

 existing ones becoming calcified, and thus adding to 

 the thickness of all of what I designated membrani- 

 form bones. My two terms are practically identical 



