Vol. XXXIV. January, igi8. No. i. 



BIOLOGICAL BULLETIN 



AUTOTOMY OF THE TAIL IN RODENTS. 



F. B. SUMNER AND H. H. COLLINS. 



It is perhaps not generally known that certain species of small 

 rodents detach portions of the tail in a seemingly voluntary 

 manner when they are seized by this member. Among the 

 mouse-like rodents of California such an autotomy of the tail 

 appears to be most typically exhibited by the pocket-mice 

 (Perognathus). 



It is the general practice of the writers, as probably of most 

 breeders of mice, to pick up their animals by the tail. This 

 appendage constitutes a convenient handle by which a mouse 

 may be lifted, commonly relieving one of the risk of being bitten. 

 But such a procedure is hazardous in the case of Perognathus. 

 By a sudden gyratory movement of the body, the tail is likely 

 to be severed at some point in its length, allowing the animal 

 to make its escape and giving the pursuer something of a handi- 

 cap in the race. 



The whole performance is so suggestive of what occurs in 

 many lizards that the question naturally arose in our minds: 

 Can it be possible that autotomy, in the one case, as in the 

 other, is followed by regeneration? This of course was not to 

 be expected in a mammal, but the experiment seemed at least 

 worth trying. In any case, the act and its consequences were 

 thought to be worthy of a brief consideration. 



The species upon which most of these observations were con- 

 ducted was a rather large pocket-mouse, Perognathus fallax fallax 

 Merriam, which is very common in the neighborhood of La 

 Jolla. Despite the frequency of autotomy in this species, we 

 soon found that all individuals cannot be depended upon to 

 "perform" when desired. Those, in particular, which have been 

 kept captive for some time seem to lose the tendency. More- 



