EXTERNAL CHARACTERS OF BLUE WHALES 311 



a curve for this measurement from a somewhat larger number of readings by taking all 

 Blue females between 23 m. and 28 m. instead of, as before, between 25 m. and 27 m. 



In Figs. 45, 46, 47 and 48 these revised curves are shown. Those for measurements 

 Nos. 13, 15 and 17 are constructed on readings from whales of all sizes, while that 

 for No. 20 is on readings from whales between 23 m. and 28 m. 



It is now seen that the curves of Nos. 15, 17 and 20 have resolved themselves into 

 more or less normal frequency curves, and that the two peaks which appeared previously 

 were therefore due only to insufficient data. As to measurement No. 13 it has been 

 found on further investigation and from information recently received from Mr Fraser 

 at South Georgia, that the two peaks in the curves result from the fact that the 

 measurement has been taken sometimes before and sometimes after flensing, and it 

 appears that this process displaces the penis so as to shorten the distance between 

 it and the anus. The same phenomenon occurs in Fin whales and for purposes of 

 comparison the curve for this species is also shown in Fig. 45. 



COLOUR 



Various descriptions have from time to time been given of the colouring of Blue 

 whales from the North Atlantic. Of these the best seems to be that of True (1904), 

 who gives an exhaustive general description and detailed notes of the nature and 

 variations of the pigmentation of twenty-two Blue whales examined by himself. 

 Barrett-Hamilton made brief notes on some half-dozen of the Blue whales he 

 examined, but it appears that no thorough account of the colouring of these whales 

 from the southern hemisphere has yet been given. 



The following is based on our own observations on whales of the South Atlantic : 



The pigmentation of Blue whales is subject to considerable individual variation, and 

 the majority of the records we have made in respect of this character have dealt simply 

 with the more variable features. 



Except on the under surface of the flippers the Blue whale's body is covered nearly 

 all over with a groundwork of dark blue-grey which varies to some extent in depth of 

 colour in diff'erent individuals. Most of the body is covered with a pale mottling which 

 consists of small, roughly oval marks of a colour which is similar to, but lighter than 

 the blue-grey background. Typical examples of these spots are shown in Plate XXVII, 

 figs. I and 2. Plate XXXVII, fig. 4, gives a close-up view of part of the back of the whale 

 shown in Plate XXVII, fig. i, taken at a point just opposite the reflexed flipper. These 

 pale spots show a good deal of individual variation in respect of their size, number and 

 sharpness of contrast with the darker background. They rarely appear on the head 

 (see Plate XXVIII, fig. i) and are not commonly present on the mandible, flippers or tail 

 flukes. They are most thickly distributed along the flanks from the eye back to the tail 

 and are often very numerous in the shoulder region. Their normal arrangement here is 

 shown in Plate XXVIII, fig. i . These marks are on the average about 4 in. long by about 

 3 in. wide, but vary in different individuals and on different parts of the body. For 



