1883.] on Whales, Past and Present, and their Probable Origin, 7 



able fact, first demonstrated by Geoffroy St. Hilaire, and since amply 

 confirmed by Cuvier, EscJiricht, Julin, and others, that in the fa^tal 

 state they have numerous minute calcified teeth lying in the dental 

 groove of both upper and lower jaws. These attain their fullest 

 development about the middle of foetal life, after which period they 

 are absorbed, no trace of them remaining at the time of birth. Their 

 structure and mode of development has been shown to be exactly that 

 characteristic of ordinary mammalian teeth, and it has also been 

 observed that those at the posterior part of the series are larger, and 

 have a bilobed form of crown, while those in front are simole and 

 conical, a fact of considerable interest in connection with speculations 

 as to the history of the group. 



It is not until after the disappearance of these teeth that the 

 baleen, or whalebone, makes its appearance. This remarkable struc- 

 ture, though, as will be presently shown, only a modification of a part 

 existing in all mammals, is, in its specially developed condition as 

 baleen, peculiar to one group of whales. It is therefore perfectly in 

 accord with what might have been expected, that it is comparatively 

 late in making its appearance. Characters that are common to a 

 large number of species appear early, those that are special to a few, 

 at a late period ; alike both in the history of the race and of the 

 individual. 



Baleen consists of a series of flattened, horny plates, several 

 hundred in number, on each side of the palate, separated by a bare 

 interval along the middle line. They are placed transversely to the 

 long axis of the palate, with very short spaces between them. Each 

 plate or blade is somewhat triangular in form, with the base attached 

 to the palate, and the apex hanging downwards. The outer edge of 

 the blade is hard and smooth, but the inner edge and aj)ex fray out 

 into long, bristly fibres, so that the roof of the whale's mouth looks 

 as if covered with hair, as described by Aristotle. The blades are 

 longest near the middle of the series, and gradually diminish towards 

 the front and back of the mouth. The horny plates grow from a dense 

 fibrous and highly vascular matrix, which covers the palatal surface 

 of the maxillse, and which sends out lamellar processes, one of which 

 penetrates the base of each blade. Moreover, the free edge of each of 

 these processes is covered with very long vascular thread like papillae, 

 one of which forms the central axis of each of the hair-like epidermic 

 fibres of which the blade is mainly composed. A transverse section 

 of fresh whalebone shows that it is made up of numbers of these soft 

 vascular papillas, circular in outline, each surrounded by concen- 

 trically arranged epidermic cells, the whole bound together by other 

 epidermic cells, which constitute the smooth cortical (so-called 

 " enamel ") surface of the blade, and w^hich, disintegrating at the free 

 edge, allows the individual fibres to become loose and to assume the 

 hair-like appearance spoken of before. These fibres difter from hairs 

 in not being formed in depressed follicles in the enderon, but rather 

 resemble those of which the horn of the rhinoceros is composed. The 



