lO BROOKLYN MUSEUM SCIENCE BULLETIN 3. I. 
This species sometimes follows sailing vessels for da\s or even weeks 
in tropical and warm-temperate seas. It is quickh- attracted b>' the 
smell of blood and decomposing flesh, a fact of which Florida shark 
fishermen take advantage b>' using rank meat and slaughter-house offal 
to entice the blue sharks within striking distance of a lily-iron. The 
skin of this and related species makes the toughest of all leathers, 
particularlv suitable for the manufacture of baggage ; but the commercial 
])ossibilities of shark fishing have hardly yet been realized. The color of 
the .skin in life is a wonderfully intense blue, a hue, however, that fades 
and becomes leaden as the skin dries. 
The teeth of the blue shark are razor-keen, and tho.se of the uj^per 
jaw finely serrated. As in most of its relatives { Carcharliiniis, Carcharo- 
don, hums, etc.), the functional teeth stand erect on the edges of the 
jaws in a single, or apin'oximatel\' .single, row. As the.se teeth become 
worn and lost, the membrane from the inner surface moves over the edge 
of the jaw, carrying with it fully developed teeth of a new, .secondary 
row. The bases of the.se new teeth are imbedded in the membrane, and 
the teeth are erected b}- mechanical stress as the membrane draws the 
row abruptly over the edge of the jaw. Thus at an\- given time there 
are behind the functional row of teeth a .series of reserve rows l>'ing re- 
cumbent one below the other on the inner surface of the jaw, with their 
])oints downward or backward. The teeth of the first or uppermost 
reserve row are develoj^ed and ready to move into the ])lace of their 
predecessors ; the teeth of the lower rows are progressively smaller and 
less develojied. The.se rows of incipient teeth are ]-)rotected by a broad 
band of membrane that extends u]) over them from the ba.ses of the 
jaws.*" 
During a cruise in the sperm whaler Daisy of New Bedford, one of 
the writers had an opportunity to .see hundreds, even thousands, of blue 
.sharks over a wide .stretch of the tropical Atlantic. Whenever a whale 
was killed, the sharks would uncannih' begin to congregate, like hyenas 
round a dead lion, as.sembling .so rapidly that the .sea would be fairl>- 
alive with them by the time the whale had been towed along.side the shiji. 
The hungry troop would then file silenth' and .slowly along the whale's 
length, fondly rubbing tail fins again.st his black hulk, and doubtless 
anticipating the fea.st of the " cutting in." During the execution of this 
process, when the water for an acre aroiuid the shi]) was stained a ghastl\- 
(>■ See Bridj^e, Cambr. Nat. Hist., Fishes, 1904, p. 251 
