Mammals 39 



It will be obvious from the above that the anatomy of our 

 rodents affords a fine field for study to any one who cares for such 

 investigations, with every prospect of making real contributions 

 to science. The matter is particularly important just now, be- 

 cause the whole classification of the rodents is in process of revision, 

 and every freshly-discovered character has its value and its 

 influence. 



Another branch of anatomy which is full of interest, but has 

 been strangely neglected, relates to the auditory ossicles.* These 

 little bones exhibit great diversities of structure, and are some- 

 times very remarkable indeed. There seems to be a definite 

 relation between the size and shape of the ossicles and the voice 

 of the animals. Some of the chirping Orthoptera (long-horned 

 grasshoppers), much preyed on by mice, produce such high notes 

 that they are inaudible to some human beings. It may be of 

 advantage to the Orthoptera to be able to call one another in notes 

 so shrill that to some animals they are inaudible, but it may also 

 be advantageous to the mice to have ears well fitted for hearing 

 those high sounds. 



It was just stated that the classification of rodents was in 

 process of revision. A Synopsis of the Supergeneric Groups of 

 Rodents, by G. S. Miller and J. W. Gidley, was published in the 

 Journal of the Washington Academy of Sciences, 1918. It is only 

 an outline of a proposed much larger work, but it opens up the 

 whole question of rodent classification in a new way, and is at 

 least of great importance. In the first place, these authors sepa- 

 rate the rabbits and pikas or conies from the rodents altogether, 

 as an order Lagomorpha. The true rodents have only two in- 

 cisors in the upper jaw, the Lagomorphs have four, and hence 

 cannot well be derived from them. The earliest available fossils 

 do not serve to connect the two groups, which have certainly been 

 separated for many millions of years. No one can deny that the 

 Lagomorphs have many distinctive characters, and it is suggested 

 that their resemblance to the true rodents is the result of con- 

 vergence rather than actual relationship. For our purposes we 

 may still regard the rabbits and pikas as rodents, but the argument 

 for their separation should not be forgotten. 



*For details see Bull. Amer. Mug. Nat. History, XXXIII (1914) pp. 347-380; XXXV 

 (1916) pp. 531-532; Zool. Anzeiger, XLIV (1914) pp. 433-440. 







