340 NATURAL SCIENCE. May, 



Probably many or most readers of Natural Science are aware 

 that the Rodents treated of have deep pouches in their cheeks, open- 

 ing externally, but no one has hitherto known exactly how these 

 pouches were utilised. Dr. Merriam tells us that they are for carry- 

 ing food into store, and that the bits of potato, apple, or what-not are 

 pushed into the pouch with the long claws of one fore-paw, while the 

 other holds the pouch open, and that they are emptied again by being 

 compressed by the paws against the cheeks from behind forwards, so 

 that their contents are squeezed out of them on to the ground in front 

 of the animal's mouth. 



Another point of interest is the use of the tail. Gophers habitu- 

 ally run backwards along their burrows almost as freely as forwards. 

 In so doing they use the short and nearly naked tail as a tactile organ 

 to guide their footsteps, a use, so far as is recorded, quite unique in 

 the Mammalia, although from its suitable length one might suspect 

 that moles' tails are similarly used. 



In the structural portion we are given a very full account of the 

 skull ; the forms of its individual bones and their methods of ossifi- 

 cation, and its changes of form with age. 



But the most interesting point of this part of Dr. Merriam's book 

 is the account of the teeth, and the discovery of the remarkable 

 method in which the molars are strengthened with enamel-plates. 

 In all other rootless-toothed rodents, so far as is known, the outer 

 walls of the molars are completely invested with a continuous coat of 

 enamel, of approximately equal thickness all round, however much it 

 may be grooved or infolded, and continuous on all sides equally with 

 the original enamel-cap of the unworn tooth ; but in Geomys the 

 enamel investment of the top thins out and disappears on the sides at 

 certain points, so that when the connecting-cap has been worn off the 

 top, which takes place at a very early age, the enamel is merely 

 present in vertical strips or plates unconnected with each other, and 

 the positions of these are treated by Dr. Merriam as of considerable 

 systematic importance. At the same time, it should be noted that 

 out of the small number of skulls available for examination in this 

 country we have found two marked exceptions to Dr. Merriam's 

 enamel-plate characters, and are, therefore, surprised to find no 

 mention of any variability, in this respect, among the enormously 

 larger series examined by him. 



In the systematic part of the work old-fashioned naturalists will 

 find more to object to, mainly in regard to the extreme generic and 

 specific splitting employed. For of the one old genus Geomys Dr. 

 Merriam now makes nine, partly on the characters of the enamel- 

 plates, and partly on those observable within the brain case, a region 

 somewhat awkward to examine for those who have not material 

 sufficient to justify them in cutting open a skull of each species, 

 although, of course, this is no argument against the soundness of the 

 conclusions arrived at. Of species and subspecies, thirty-seven are 

 admitted, no less than twenty-one being new, numbers which contrast 

 somewhat strikingly with the seven recognised by Baird in 1857, 

 these even having been reduced to five by Coues in 1877. Still, it 

 must not be supposed that any considerable proportions of the thirty- 

 seven species are mere " splits" of those previously known, as a most 

 astonishing number of genuinely distinct forms have been discovered 

 by recent collectors in Mexico, and mainly by Mr. E. W. Nelson, of 

 the Department of Agriculture, during his exploration of Mexico in 

 1892 and 1893. 



The book, as a whole, is exceedingly well illustrated, the nineteen 



