1895 THE MICROSCOPE. 117 



the higher orders, be examined with a high power, it 

 will be found to consist of three layers. The uppermost 

 is composed of several concentric laminae, the outside 

 one being the smaller, and they increase in size, each be- 

 ing a little larger than the one above it, so that their 

 margins appear on the surface as a series of concentric 

 lines and their surfaces are thrown into furrows and 

 ridges. It is these laminae which we see, and in some of 

 the furrows the laminae have entirely separated showing 

 the layer beneath them. 



Sometimes in Cycloid scales the pigment cells can be 

 seen giving the scale a spotted appearance, as in the 

 Carp (fig. 2) and Eel (fig. 14). 



The GtANOID. — These scales are usually bony, often 

 having the same structure as the bones of the fish to 

 which they belong. They are usually angular in form 

 and arranged in rows, the scales but slightly overlaping 

 one another, thus forming a coat of armor. To this order 

 belong the Sturgeon, Lepidosteus and Hassar-fish, but 

 most of this order are found in the fossil state. 



The Placoid. — To this order belong the Skate, Dog- 

 fish, Ray and Shark, besides many fossil allies. These 

 are not like the scales we have been examining, but are 

 more like teeth and project from the skin as spines. 

 They are much like teeth in structure and are covered 

 with a hard enamel resembling the enamel of teeth. 

 Fig. 1 represents a piece of the skin of the Thornback 

 Skate, showing spines and pigment cells. It can be 

 mounted dry without a cover-glass and viewed as an 

 opaque object and also with transmitted light, and the 

 polariscope. I know of no objects so easily obtained 

 and mounted which will furnish more entertainment for 

 one's friends than the scales of fishes. Fine mounts of 

 scales can be obtained of Rev. J. D. King, Cottage City, 

 Mass, 



