ORDEES OF MAMMALIA, 



329 



there is a dorsal fin as well. The nostrils may be single or double, 

 but always are placed on the top of the head, constituting the 

 "blow-hole." The body is very sparingly furnished with hairs, or is 

 wholly without them in the adult. The head is generally of dis- 

 proportionately large size as compared with the body, and is rarely 

 separable from the trunk by any distinct constriction or neck. 

 There is no sacrum ; the pelvis is only represented in a rudi- 

 mentary form ; and. the hind-limbs are either wholly wanting, or 

 are present only as rudiments, : concealed within the muscles. 

 Lastly, the adult is either wholly destitute of teeth, or possesses 

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

 divisible into distinct groups. All the true Cetacea are carnivorous, 

 living upon animal food. 



Chief amongst the Cetaceans in importance and zoological interest 



Fig. 2?..'>.— Spprinaf-oti MHiale (rjtjf^efcr vTnrrorrpJtnJv^). 



are the "Whalebone Whales {Ba/cenidw), in which the adult is desti- 

 tute of teeth, though the young Whale possesses 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 Mol- 

 luscs and Jelly-fishes upon which these enormous animals live. The 

 most important member of this familj^, from a commercial point of 

 view, is the Greenland Whale {Dalcena 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 enor- 

 mous 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 



