Glass 6. Mammalia. Order 10. Cetacea. 523 



portion there are several perpendicular notches reaching to the base. 

 The plates, of which the tirst and last of each row are the smallest, lie 

 fairly close together on each side, and fill up a large portion of the 

 buccal-cavity, in the middle of which, however, a space, triangular in 

 transverse section, persists. When the mouth is closed, the whalebone 

 is covered by the lower jaw : it serves as a filtering apparatus ; the 

 Mystacoceti swim for some distance with the mouth gaping open, then 

 close it, and the water trickles out between the baleen, leaving the 

 contained organisms imprisoned by the fibrous inner edge of the 

 blades. The whalebone is to be regarded as extraordinarily well- 

 developed palatal ridges [see p. 487). The salivary glands are 

 rudimentary or absent, the stomach is complex. The larynx extends 

 forwards as a tubular prolongation, surrounded by the well-developed 

 soft palate ; thus a continuous passage between nostrils and trachea is 

 formed, on either side of which the food passes into the oesophagus. 

 The testes are retained in the abdominal cavity. 



The Whales are almost all marine ; some few occur in rivers. Like 

 Fish, they move by undulations of the tail, and never voluntarily come 

 on to land. They are able to remain for considerable periods below 

 the water (half an hour or more) . Their food consists chiefly of Fish 

 and marine Invertebrata. They frequent all seas, the large forms, 

 however, occur chiefly in the colder regions of the world. The largest 

 animals known belong to this group. 



Sub-Order 1. MystaCOCeti {Whale-bone Wltales). 



Edentulous, but provided with whale-bone. Two external nares, 

 placed more anteriorly than in the Odontoceti. Only one pair of true 

 ribs. The skull is extraordinarily large and bilaterally symmetrical ; 

 nasals relatively well-developed. The Mystacoceti feed on various 

 small marine animals, which live in shoals (Euphausidse, Gopepoda, 

 etc.) ; many of the Balsenoptera also feed upon small Fish. This sub- 

 order includes the largest Whales. 



1. The Pin-whales (Balsenopteridse). With dorsal fin. On the ventral 

 siu-face of the head and body, there are numerous deep longitudinal grooves. 

 Elongate animals, with relatively small head and short whalebone ; naiTow 

 pectoral fins. The Blue-whale or Sibbald's Jb'in-whale (Balxnoptera 

 Sibbaldii), which attains a length of about .30 m. ; and the rather smaller 

 Rorqual {B. musculus), which is abundant in North European seas, are not 

 uncommon off British coasts. Both of these are the objects of a legular 

 fishery on the coasts of northern Norway. The Lesser Pin-whale {B. 

 rostrata) is much smaller (the largest only 10 m.) and also occurs in the North 

 Atlantic. The very large Hump-back Whale {Megaptera hoops), with low 

 hump-like dorsal fins and with very long pectoral fins, is less elongate than 

 most other Balsenoptera ; a few have been taken off British coasts. 



2. Balaenidse, No dorsal fin ; no ventral furrows ; body less elongate ; 

 head relatively very large ; whalebone long and narrow ; pectoral fins broad. The 



