MOVEMENTS BENEATH THE SURFACE 131 



possible advantage of this to an organism in need of turning sharply to right and left is suggested by 

 the results obtained by Harris (1936) on the dorsal fins of fish, and it seems probable that the fins of 

 rorquals are in no way analogous to the fins of these other cetaceans. 



As compared to the ease with which rorquals are able to turn sharply upwards or downwards, 

 their movement from side to side appears to be restricted. This is suggested both by the structural 

 arrangement of the fins, flukes and flippers, and also by the behaviour of Fin whales when feeding. 

 Their habit of turning on to their sides when moving about among small patches of food has often 

 been recorded (Millais, 1906, p. 255), and Andrews (1909, plate XL, fig. i) has photographed a whale 

 in this position. This seems most probably to be a turning movement. The very localized and irregular 

 distribution of the krill must demand a twisting motion which is probably beyond these whales in their 

 normal swimming position. The flattened head and laterally extended flukes, while they are evidently 

 well adapted for the purposes of turning upwards or downwards to and from the surface, seem in- 

 capable of giving an equally sharp turn to right or left : like an aeroplane it has to bank. 



III. COMPARISON WITH EARLIER ACCOUNTS 

 True (1903) and Allen (1904) give brief descriptions of Finbacks off Newfoundland which agree well 

 with the type of movement described on pp. 1 1 6, 1 1 7. True, however, reports having seen little or nothing 

 of the back behind the dorsal fin, although the whales are described as having come up to the surface 

 obliquely and as exhibiting strong curvature (p. 92). On some points, however, True's photographs 

 differ from the text. In his plate XXV, fig. i , a relatively short length of back shows above water as 

 its curvature and the position of the head clearly indicate. The fin is still well submerged ; yet True 

 states that ' The whole upper surface of the body from about the middle of the head to the dorsal fin 

 is above water. . . '. The text suggests that in fig. 2 the dorsal fin is hidden by a wave, but the position 

 of the whale shows clearly that the fin itself is outside the picture and is probably still below water. 



Both True and Allen note the lowering of the head and the arching back, but neither draws attention 

 to the fact that the back rises out of the water, nor that the wheeling motion slows down. Millais 

 (1906, p. 268), however, states 'The Finback simply lifts itself a little higher and goes down smoothly 

 and silently and goes down at an oblique angle', and Andrews (1909, p. 216) makes a similar remark. 



Racovitza (1903) distinguishes between two types of action at the surface, the one concerned with 

 the longer and deeper dive which he terms ' La Sonde ' and the other with ' Les plongements inter- 

 mediaires '. According to Racovitza, inspiration and expiration are deeper before and after sounding 

 than before the intermediate dive, but comparative data are not given. Again, the intermediate dives 

 last a few minutes, whereas sounding seldom lasts less than a quarter of an hour, but more precise 

 data are not given. The whales are also said to dive more shallowly intermediately than when sounding, 

 though how the depth of the whale was judged during the minutes it was out of sight is not made 

 clear. And lastly, the curvature of the back is held to be greater before sounding than before the 

 intermediate dive. Racovitza ascribes a regularity to these movements which the present writer 

 finds impossible to accept ; they will be considered in further detail. 



His first point (p. 6) that ' L'expiration se produit exactement au moment ou le sommet de la 

 tete, . . . arrive a la surface ' does not reckon with the habit Fin whales sometimes have of blowing oflF 

 air while the blowhole is still submerged (see p. 117), which appears also to have been noted by Howell 

 (1930, p. 91). And his claim that ' C'est la bosse de I'event qui signale I'animal' can be accepted only 

 for those whales which approach the surface in a more or less horizontal position. Such whales 

 appear to have been observed by Allen (1904, p. 615). 



Racovitza has allowed 5-6 sec. for the duration of the blowing, which is greatly in excess of our 



