OUDEliS OF MAMMALIA. 



329 



there is a dorsal fiu :ui well. Tlie r.(;r;trils may Le Kiiigle or douUe, 

 but always are placed on the to;! 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 comjiared with the body, and is rarely 

 separable fi-oni the trunk by any distinct constriction or neck. 

 There is no sacrum ; the jielvis is only lepresented in a ludi- 

 mentary form ; and the hind liml.is are either wholly wanting, or 

 are present only ar, rudiments, concealed within the muscles. 

 Lastly, the adidt is either wlioUy de.stitute of teeth, or jiossesses 

 only a single set, which are always conical in sha])e, and are never 

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

 living upon animal focjd. 



Chief amongst the Cetaceans in importance and ijoological interest 



Fig. 235. — Sliermaccti WHiale {Pliji?rtrr mncroccphahis). 



are the Whalebone Whales [Balcenicla), in which the adidt 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 wdialebone or hatccn, wdiich are used as a kind of screening 

 apparatus or filter to separate from the sea-water the minute Mol- 

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

 most important member of this fanuly, from a commercial point of 

 view, is the Greenland Whale {Daltvna mi/sticetiis), 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 " Ijlubbcr," which is situated 



