MONSTROSITIES 283 



nerve-centres to produce asymmetry of the two sides. And one 

 can imagine that a slight difference in the circulation of the two 

 halves of the nervous system might cause this want of exact 

 symmetry. 



The examination of the two sides of spotted and striped 

 animals, such as those of Figs. 4 and 22, will convince any one that 

 a mathematical symmetry of both sides of an animal, if it occurred 

 at all, must be rather the exception than the rule. 



Professor Flower has stated that in the Cetacea, even the two 

 hands may have a different number of bones}- 



In the Royal Natural History, vol. ii. p. 143, there is the 

 description of a very interesting phenomenon, because evidently 

 rarely met with. The writer says : ' One of the two known skulls 

 of Ross's Seal is peculiar in that, while on one side the first upper 

 cheek-tooth, and both the corresponding lower teeth, are imper- 

 fectly divided by a vertical groove, on the opposite side of the 

 upper jaw the place of this tooth is taken by two complete single 

 teeth. Hence it is obvious that we have here a case where an 

 originally single tooth divides into two distinct but simpler teeth. 

 . . . This serves to show how the numerous simple teeth character- 

 istic of the toothed Whales may have been derived by the splitting 

 up of teeth originally composed of three distinct cusps, like those 

 of the Leopard Seal, each cusp of such tooth forming, as we shall 

 see, a distinct tooth in the Whales.' 



The writer mentions other peculiarities in the teeth of the Grey 

 Seal on pp. 134, 135. 



All this is very instructive, not only because it shows us that 

 on one side of the same jaw there may be simple teeth, while on 



1 ' Sometimes the different sides of the same animal are not precisely alike, either 

 in the arrangement or even the number of the carpal ossifications.' Osteology of 

 Mammals, p. 301. 



