ARMOUR-CLAD WHALES 309 



have developed a dermal armour which would serve to 

 protect them alike from the breakers and from the attacks 

 of sharks and other marine monsters. For the idea that 

 the terrestrial ancestors of the cetaceans were clad in 

 armour cannot for a moment be entertained, since the 

 primitive mammals were not so protected, and the American 

 armadillos afford an instance of the development de novo 

 of such a bony panoply at a comparatively recent 

 epoch. 



Years ago the late Dr. H. Burmeister described a porpoise 

 from Argentina as Phocacna spinipinnis, on account of its 

 possessing a number of spiny tubercles embedded in the skin 

 in the neighbourhood of the back-fin as well as on the fin 

 itself. " Some small spines," he wrote, " begin in the middle 

 of the back, at the distance of twenty-five centimetres 

 in front of the fin, as a single line of moderate spines ; 

 but soon another line begins on each side, so that in the 

 beginning of the fin there are already three lines of spines. 

 These three lines are continued over the whole rounded 

 anterior margin of the fin and are augmented on both sides 

 by other small spines irregularly scattered, so that the whole 

 number of lines of spines in the middle of the fin is five." 

 In a section of the skin of the back-fin the tubercles are 

 distinctly seen, many of them being double. 



Similar tubercles were described on the back-fin of a 

 porpoise taken in the Thames in 1865 ; and quite recently 

 a row of no less than twenty-five well-developed tubercles 

 has been detected on the front edge of the back-fin of a foetal 

 porpoise, these tubercles being nearly white and thus showing 

 up in a marked contrast to the dark-coloured skin. Even 

 more distinct are the tubercles in the skin of the finless 

 back of the Japanese porpoise, where they form several 

 rows of polygonal plates. 



