Our knowledge of the Whalebone Whales, the largest of all mammals, has 

 hitherto been, and still is, very imperfect, notwithstanding the publication 

 in later times of several treatises on that subject, which possess great merit, 

 and materially contribute to dissipate the darkness, that has hitherto enve- 

 loped that portion of zoological science. Later observations have shown, 

 that the number of species comprised in that group is by no means so small 

 as had been supposed, as also that those, which occur in the Southern or 

 Antarctic, are always different from those, which belong to the Northern 

 Ocean. Since it was proved by the late Professor Eschricht that they 

 make periodical migrations, it has been evident, that several species, that 

 pass the milder season of the year in the North Polar seas, emigrate to the 

 south in the colder season, and are occasionally met with in waters far 

 south of their natural zone, e. g. Physalus musculus Companyo, or Phys. 

 antiquorum Gray in the Mediterranean; but, as far as we are aware, they 

 never extend their wanderings to the equatorial-regions, nor do those which 

 belong to the Southern ocean ever enter the waters north of the equator. It 

 is however evident, that, in consequence of this, the geographical distribu- 

 tion of the species is very extensive. On this subject much yet remains to 

 be investigated, and it is possible that closer examination and comparison 

 may show differences between species that have been hitherto considered as 

 identical. 



As this distribution appears to be dependent on temperature, for some 

 species belong to the polar and others to the warmer seas , it is evident that 

 under the different relations of temperature that prevailed in ancient ages, 

 the distribution must have been different from what it is at the present time. 



