xv BALEEN OR WHALEBONE 217 



tions it is impossible, in the imperfect state of our knowledge 

 of the habits of the Cetacea, to explain, but the fact that in 

 almost every case a more full number of rudimentary teeth is 

 present in early stages of existence, which either disappear, or 

 remain as concealed and functionless organs, points to the 

 present condition in the aberrant and specialised forms as 

 being one derived from the more generalised type, in which 

 the teeth were numerous and equal. 



The Mystacocetes, or whalebone whales, are distinguished 

 by entire absence of teeth, at all events after birth. But it is 

 a remarkable fact, first demonstrated by Geoffrey St. Hilaire, 

 and since amply confirmed by Cuvier, Eschricht, Julin, and 

 others, that in the foetal 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 have 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 simple 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 remark- 

 able structure, 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 trans- 

 versely to the long axis of the palate, with very short spaces 

 between them. Each plate or blade is somewhat triangular 



