ITS STRUCTURE, BULK, AND ASPECT. 



77 



tition of this ancient ganoid : it, as it were, shows us the 

 crocodile lying entrenched behind the fish. The interior 

 structure of these reptile teeth is very remartable. In the 

 longitudinal section we find numerous cancelli, ranged length- 

 -yise along the outer edges, but much crossed, net-like, within, 

 — greatly more open towards the base than at the point, — 

 and giving place in the centre to a hollow space, occasionally 

 traversed by a few slim osseous partitions. In the transverse 

 section these cancelli are found to radiate from the open cen- 

 tre towards the circumference, like the spokes of a wheel from 

 the nave ; and each spoke seems as if, like Aaron's rod, it 

 had become instinct with vegetative life, and had sprouted 

 into branch and blossom. Seen in a microscope of limited 

 field, that takes in, as in the accompanying print (fig. 34), 



Fig. 34. 

 h a 



POETION OF TRANSVERSE SECTION OF REPTILE TOOTH OF ASTEROLEPIS. 



a. Nat. size. b. Mag. twelve diameters. 



not more than a fourth part of the section, the appearance 

 presented is that of a well-trained wall-tree. And hence the 



