354 DISCOVERY REPORTS 



the V is opposite the insertion of the flippers and hes in the mid-dorsal Une pointing 

 forwards towards the snout. This mark is very noticeable in foetuses in which the 

 dorsal pigment has started to develop. 



A long black band, 2 to 3 in. wide at first but increasing in width, runs backwards 

 and upwards from the eye (see Plate XXXIV, fig. 3). The asymmetry of the pigmentation 

 is very noticeable here, for the right shoulder and right side of the head are very much 

 paler than the left, and in consequence the black band stands out in great contrast on 

 the right side, while on the left it can hardly be said to exist, since almost the whole 

 shoulder region is pigmented. 



On the whole, there is little individual variation in the pigmentation of Fin whales 

 except around the ventral region posterior to the anus, and perhaps in the degree to 

 which the pigment of the flanks extends over the ventral thoracic region. The restriction 

 of the ventral white area and the prominence of the projecting strips of pigment behind 

 the anus seem to go largely together and there is not really very much to say of the 

 variation of an individual Fin whale, apart from the tone of the pigment, except that 

 it is a heavily or lightly pigmented whale. 



From the descriptions given by Sars (1865) and True (1904) of the colouring of Fin 

 whales from the North Atlantic one must suppose that the whales of the North and South 

 Atlantic are very similar if not identical in colour and arrangement of the pigment. 



Pigment appears at a fairly early stage in the foetus. When the latter measures 

 0-5 m. to i-o m. it is present as a darkening of the skin on the top of the head, the 

 anterior part of the back, the tip of the dorsal fin, the dorsal surface of the flukes and 

 the outer surface of the flippers. At this stage the pigment is of a faint grey colour, 

 confined apparently only to the superficial layer of skin, while the rest of the body is 

 of a pinkish colour. As the pigment spreads backwards from the neck over the dorsal 

 surface, the pale dorsal V-mark makes its appearance. The development of the colouring 

 from now on through gestation consists in the deepening of the colour on the dorsal 

 surface and the spreading of the pigment downwards over the flanks. The dorsal 

 V-mark appears soon after the foetus measures i-o m. and it soon becomes even more 

 prominent than in the adult whale. At 1-5 m. the lower jaw is well pigmented and the 

 asymmetry of the colouring is already distinguishable. Before 3 m. is reached the 

 pigmentation is similar to that of the adult except that the colour is still rather paler 

 and the pigment has not reached so far down the flanks. 



The asymmetry of the pigment appears to be an invariable feature of the colouring 

 of Fin whales. Among northern Fin whales this asymmetry may on rare occasions be 

 reversed, as described by CoUett (19 12), the right instead of the left being the darker 

 side. No such case, however, has appeared among all the whales we have examined, 

 and if such a reversal does occur in the south it must certainly be extremely rare. 



It may be suggested, as a possible explanation of the shifting of the pigment over 

 to the left side, that Fin whales swim slightly on their right side while under the water. 

 Such a habit would seem rather peculiar, though perhaps not more so than the dis- 

 placement of the pigment. We have made attempts to test this possibility by observa- 



