60 



may have belonged. I also stated that anatomists had long been fa- 

 miliar with the fact, that in proportion to the size of the blood-cor- 

 puscles so is that of the capillaries, and of the muscular and nervous 

 fibres; and it would appear that the same thing held good with 

 respect to the bone-cells. From the highly valuable table of the 

 comparative sizes of the blood-discs, published by Mr. Gulliver, we 

 learn, that the blood-particles are largest in reptiles, smallest in Mam- 

 malia and birds, and in fishes of an intermediate size ; and it has been 

 already stated, that the bone-cells are largest in reptiles, and are 

 much smaller in Mammalia and birds ; hence it would appear, that 

 the bone-cells are subject to the same law as the capillary, muscular, 

 and other systems ; and in the advanced stages of the inquiry, it may 

 possibly turn out, that if one or other of these systems be known the 

 size of the others may be readily inferred. 



Since my last communication, of which the preceding is a brief 

 abstract, I have extended my researches to the investigation of the 

 minute structure of the bone of those Reptilia in which the blood - 

 particles are the largest, and have taken as examples some of the pe- 

 rennibranchiate Reptilia, viz., the Siren, the Proteus, the Menopome, 

 the Menobranchus, and the Axolotl, and the result of the examination 

 has been highly satisfactory, for I find, as I had predicted, that the 

 bone-cells would be the largest in those animals which had the largest 

 blood-discs. In the Siren they appear to have attained their greatest 

 size ; and this reptile, as far as I can learn, has larger blood-discs 

 than any other existing animal : the portions of bone examined were 

 taken from the skull, and from a vertebra, and these fragments exhibit 

 cells of enormous size ; some of them are oval, others of* a quadri- 

 lateral figure, with very large but not very numerous canaliculi, whilst 

 others are not so broad, but much more elongated, and the canaliculi 

 so numerous as to form a dense net-work around the cells, which 

 nearly obscures them. The latter or elongated cells are chiefly 

 found in the thick or dense portions of bone, where they are arranged 

 in parallel rows, like those of the Turtle and Python before alluded to, 

 whilst the former or broad cells occurs in the thinner plates of bone, 

 and never are arranged in rows, but are scattered irregularly about ; 

 and if the bone be recent, the granular contents of the cells will be 

 readily made out : if the specimen be a thin one, and mounted in 

 Canada balsam, it will sometimes happen that the cells contain air, 

 and in the process of mounting the balsam will enter the canaliculi 

 and obscure them, and the cell will then appear like a large bubble 

 of air, for which it has been more than once mistaken. The bones of 



