EXTERNAL CHARACTERS OF BLUE WHALES 313 



fig. 2). Though the outer surface of the flipper is nearly all pigmented the tip is 

 usually white. 



One other variable feature in the pigmentation of Blue whales appears on the under 

 surface of the flukes. The upper surface is normally of a uniform blue-grey. The under 

 surface is rather paler and in most cases shows a number of fine whitish striations 

 which run in an antero-posterior direction (Plate XXXI, fig. 3). These are not usually 

 very noticeable and sometimes are not to be seen at all. In other individuals they are 

 strongly marked, and in one case (whale No. 819) they were so pronounced that the 

 anterior half of the ventral surface of the flukes was practically white. It is a fairly 

 general rule that well-marked fluke striations are associated with a lack of pigment 

 under the flippers. 



From the photographs and description given by True of the pigmentation of Blue 

 whales from the North Atlantic it is certain that there is no important diff'erence in 

 this respect between the Blue whales of the North and South Atlantic. In fact, so far 

 as the pattern of the pigmentation is concerned, his account might be applied in almost 

 every detail to the whales we have examined in the south. 



In the foetus the first signs of external pigmentation appear when it measures about 

 0-5 m. Up to this stage the body has a uniform pinkish or greyish appearance. Now, 

 however, there is a faint darkening on the head, round the jaws and inside the mouth. 

 The pigment seems to appear first on the extremities and to spread over the dorsal 

 surface from the head backwards. At about 1-5 m. pigment can be recognized on the 

 head, rostrum and mandible, along the anterior part of the back, and on the dorsal 

 surface of the flukes. At about 2-0 m. it becomes general over the dorsal surface 

 but remains rather thin except on the head and extremities. From about 2-5 to 3-0 m. 

 all the markings of the adult pigmentation become distinguishable except on the ventral 

 surface. It is not until the length increases to 4 or 5 m. that the whole pattern is 

 completed and even the large foetuses of 5 or 6 m. remain paler than the adult with 

 less sharply defined spots and flecks. 



BALEEN 



As in the case of the colour of whales, observations have been made on the baleen 

 with the main object of studying the variations which may occur. There are also points 

 of interest in a comparison of the development of the baleen with the rate of growth 

 of the young whale. 



Routine observations included the counting of the numbers of plates, measuring the 

 length of the longest plates from base to tip (excluding the terminal bristles) and the 

 spacing of the longest plates (by measuring the average spacing of ten). A few measure- 

 ments were made of the width of the plates at the base, but this is an awkward measure- 

 ment to make and diflicult to perform accurately. 



The baleen is of great importance from the systematic point of view, for the species 

 of a whale can almost always be recognized from a single whalebone plate. In Blue 

 whales it is rather coarse and short and is of a uniform blue-black colour not differing 



