32 A BOOK OF WHALES 



commencement of the tail. In Phoccena spinipinnis 

 there are more numerous tubercles than in P. com- 

 munis, present on the back as well as on the front 

 margin of the dorsal fin. Dr. Klikenthal has pointed 

 out that these tubercles are especially large compara- 

 tively, and obvious, in the embryos of Neomeris, an 

 important fact in view of their inheritance from a 

 more completely armoured ancestor. These tuber- 

 cles have a form which is indicated in the accom- 

 panying figure. (Fig. 7.) There is a more especially 

 roughened area in the centre of each. The general 

 outline is squarish. As will be also seen in the figure, 

 these structures are by no means unlike scales. But 

 the term " scale " is one which is often used in more 

 than one sense ; it is necessary to inquire as to what 

 kind of scales these integumental tubercles of the 

 porpoises are to be likened to. The scales of a 

 lizard or a snake are simply horny thickenings of the 

 epidermis ; they are, therefore, not at all comparable 

 to the scales of such a fish as the perch or pike, 

 where the scales are calcified plates produced in the 

 dermis lying below the epidermis. In other fishes, 

 such as the sharks and rays, the scales are calcified 

 structures produced by the joint activity of both 

 epidermis and dermis. Professor Ktikenthal dis- 

 covered that the rudimentary scales of the common 

 porpoise are calcified, and that the calcification is 

 only met with in the dermis. It follows, therefore, 

 that the rudimentary dorsal armature of the porpoise 

 is comparable to the skin plates of an armadillo to 

 compare it with an animal that is nearer to it in the 



