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 Phocaena 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. 
