RAMBLES OP A GEOLOGIST. 283 



obliged to have recourse to forms of a more complex and in- 

 volved outline. These latter-day scales send out nail-like 

 spikes laterally and atop, to lay hold of their neighbours, and 

 exhibit in their under sides grooves that accommodated the 

 nails sent out, in turn, by their neighbours, to lay hold upon 

 them. Their forms, too, are indescribably various and fan- 

 tastic. It seems curious enough, that immediately after this 

 extremely artificial state of things, if I may so speak, the 

 two prevailing orders of the fish of the present day, the Cy- 

 cloids and Ctenoids, should have been ushered upon the scene, 

 and more than the original simplicity of scale restored. There 

 took place a sudden re-action, from the fantastic and the com- 

 plex to the simple and the plain. 



It is further worthy of notice, that though many of the 

 ganoid scales of the Secondary systems, including those of 

 the Wealden, glitter as brightly in burnished enamel as the 

 more splendent scales of the Old Red Sandstone and Coal 

 Measures, there is a curious peculiarity exhibited in the struc- 

 ture of many of the older scales of the highly enamelled class, 

 which, so far as I have yet seen, does not extend beyond the 

 Palaeozoic period. The outer layer of the scale, which lies 

 over a middle layer of a cellular cancellated structure, and 

 corresponds, apparently, with that scarf-skin which in the hu- 

 man subject overlies the rete mucosum, is thickly set over 

 with microscopic pores, funnel-shaped in the transverse sec- 

 tion, and which, examined by a good glass, in the horizontal 

 one resemble the puncturings of a sieve. The Megalichthys 

 of the Coal Measures, with its various carboniferous conge- 

 ners, with the genera Diplopterus, Dipterus, and Osteolepis 

 of the Old Red Sandstone, all brilliantly enamelled fish, 

 are thickly pore-covered. But whatever purpose these pores 

 may have served, it seems in the Secondary period to have 

 been otherwise accomplished, if, indeed, it continued to exist. 

 It is a curious circumstance, that in no case do the pores seem 



