61 



all the perennibranchiate Reptilia before enumerated present the 

 same form of cells, but in none do they equal in size those of the 

 Siren. 



The structure, then, of the bone of the perennibranchiate Reptilia 

 may be characterized by the almost entire absence of the Haversian 

 canals, except in the large bones, and by having their place supplied 

 by enormously long and broad, and sometimes quadrilateral, bone- 

 cells, with large canaliculi, anastomosing freely with those of neigh- 

 bouring cells : the canaliculi are large, like those of fish, but not so 

 numerous as those of the ordinary reptiles, as may be seen by com- 

 paring figs. 4, 5, and 6, with fig. 3, in Plate vii. In fact, everything 

 agrees with the characters presented to us by the blood of these ani- 

 mals. I have never yet seen the blood of the Menopome, Proteus, or 

 Axolotl, but should infer, from the structure of their bone, that their 

 discs or corpuscles, as they are termed, are not so large as those of 

 the Siren. As some of the highest authorities in comparative ana- 

 tomy are still at issue respecting the true class to which the Lepido- 

 siren belongs, some regarding it as a reptile, others as a fish, I was 

 anxious to ascertain what evidence of its true nature might be ob- 

 tained from the structure of its bone ; and I may here state, that a 

 thin fragment from the base of the cranium exhibits two forms of very 

 large cells, the one of a quadrilateral figure, like those of the Siren, 

 the other of an elongated form, similar to those of the Turtle, but much 

 greater in breadth : the first kind were distributed irregularly, and at 

 wide intervals apart from each other, whilst those of the second or 

 elongated kind were arranged in parallel rows, with a dense net-work 

 of canaliculi around them, so dense in some parts as almost to ob- 

 scure the cell : in all these characters the structure agrees with that 

 of the bone of the perennibranchiate Reptilia just described, no cells 

 at all resembling them having as yet been found in any of the orders 

 of fishes. The cells of the latter animals which come nearest to those 

 of Reptilia are depicted in Plate vii. fig. 4 ; they are from the Conger 

 Eel, and are elongated like those of the Turtle, but have not the 

 breadth, nor so great a number of canaliculi as those of the latter 

 animal, and they are so entirely different from the cells of any of the 

 perennibranchiate Reptilia, that not a moment's hesitation need be 

 required to satisfy an inexperienced observer of their want of identity. 

 The elongated cells are rarely to be found, except in the bones com- 

 posing the endo-skeleton of fishes: in the scales, and other thin 

 plates of osseous matter, the cells are of a small quadrilateral figure, 

 and have but few canaliculi, as may be seen in Plate viii. fig. 1, 



TRANS. MIC. SOC. VOL. II. F 



