OEDERS OF MAMMALIA. 295 



a single set, which are always conical in shape, and are never 

 divisible into distinct groups. All the true Cetacea are car- 

 nivorous, living upon animal food. 



Chief among the Cetaceans in importance and zoological 

 interest are the Whalebone Whales {JBalcenidoe), in which 

 the adult is destitute of teeth, though the young whale pos- 

 sesses teeth which never cut the gum. The place of teeth is 

 taken by a series of transverse plates of whalebone or baleen, 

 which are used as a kind of screening apparatus or filter to 

 separate from the sea-water the minute MoUusks and Jelly- 

 fishes upon which these enormous animals Uve. The most 

 important member of this family, from a commercial point of 

 view, is the Greenland Whale {Balmna mysticetus), which 

 yields most of the whale-oil and whalebone of commerce. The 

 Greenland Whale attains a length of from forty to sixty feet, 

 and of this enormous length about a third is taken up by the 

 head alone. The oil is derived from a thick layer of fat or 

 " blubber," which is situated under the skin, and serves to pro- 

 tect the animal from cold. Though an inhabitant of the sea, the 

 whale is obUged to come to the surface to breathe, and in so 

 doing it ejects from the blow-holes what looks like a column 

 of water, the whole operation being known to the whalers as 

 " blowing." The true nature of this act is still somewhat 

 questionable, but it appears certain that the apparent jet of 

 water is in reality, mainly if not entirely, due to the condensa- 

 tion of the moisture which is contained in the air expelled from 

 the lungs. The old view was that " blowing " consisted in 

 the whale ejecting through the nose the water which had pre- 

 viously been filtered through the baleen-plates of the mouth ; 

 but it appears to be quite certain that this view, at any rate, 

 is not the correct one. The Rorquals or Finner Whales re- 

 semble the Greenland Whale in most respects, but the skin is 

 furrowed with deep plaits or folds, and there is a dorsal fin, 

 placed on the back. Some of these attain a gigantic size 

 (eighty feet or more), but the}' are seldom captured, as their 

 commercial value is small. 



The Toothed Whales ( Odontoceti) are best known by the 

 Sperm Whale, an animal as large as, or larger than, the Green- 

 land Whale, but distinguished by having numerous conical 

 teeth, a single blow-hole, and a curiously-truncated head. 

 They yield an excellent oil, and the singular fatty substance 

 which is known as " spermaceti." They also yield the sub- 

 stance called " ambergris," which is used as a perfume ; but 

 this is probably a product of disease. 



