Origin of the Dentition of the Rodentia. 3 
night. The largest of these fishes, which were all of the same spe- 
cies, were nine to ten inches in length, and having been taken 
immediately from the beak of the bird were scarcely bruised. The 
largest and best of. these we had the next morning for breakfast, 
the others we gave to our friend, the cormorant, who was kindly 
assisted by his master to get them past the curd which constricted 
his throat so that he could not otherwise have swallowed. 
The birds are trained especially for the work, and do not fish 
in the day-time. Our bird was two years old, and was considered 
a very bright and active fisher, having on good nights, fishing all 
night, caught as many as 400 fishes,—300 was considered a fair 
night’s work. Only calm nights are available, and the darker the 
better. 
THE MECHANICAL CAUSES OF THE ORIGIN OF 
THE DENTITION OF THE RODENTIA. 
BY E, D. COPE. 
Nea phylogeny of the Rodentia as an order is now tolerably 
clear. I at first suggested,' and later asserted, that this order 
_ was derived by descent from the Tillodont suborder of the Buno- 
theria. The Tillodont suborder had a common origin with the 
Tzeniodonta, from some type of Bunotheria with unspecialized 
motars and premolars, in which some of the incisor teeth had begun 
to display enlarged size. A form allied to this ancestor is the genus 
Esthonyx, which differs from it in but few respects. Professor 
Ryder, in discussing the origin of the Rodentia,” writes as follows : 
“The significance of accessory rudimentary incisors present in some 
forms of true rodents, as pointing to the manner in which the evo- 
lution of the rodent type of dentition took place, may be overrated ; 
yet when it is borne in mind that in other groups the appearance of 
diastemata between the different kinds of teeth took place gradually 
and in a way which unmistakably shows the gradual steps of the 
1 American Naturalist, April, 1883; Report U.S. Geol. Surv. Tertiary 
Vertebrata, 1885, 814; American Naturalist, April, 1884. 
* Proceed. Academy Philada., 1877, p. 317. 
