ON TOOTH-GENESIS IN THE CAVIID®. 261 
-Toors-Genests IN THE Cavitpm. By H. W. Marzrr Try, 
B.A., M.D., F.LS., F.Z.S., Lecturer on Biology and Com- 
parative Anatomy, Charing Cross Hospital Medical School; 
Lecturer on Zoology, Bedford College, London.* 
[Read 17th January, 1901.] 
(PLATE 26.) 
THoveH much has been already written concerning the dentition 
of the Rodentia, no paper has yet appeared, so far as I am aware, 
dealing with the tooth-genesis of that Order. Previous research 
has been mainly, if not entirely, in the direction of attempts to 
discover the germs of teeth no longer functional in the adult, 
more particularly in the region of the diastema and premaxilla, 
and thereby to endeavour to homologize the existing incisors of 
the Rodents with those of other mammals. 
The morphological value of an enquiry into the tooth-genesis is 
due to the fact that several views have been advanced from time 
to time to account for the origin of the complex crown of the 
mammalian molars from the Haplodont type of tooth. 
In 1896, in a paper dealing with the tooth-genesis in the 
Canide [22), 1 adopted the suggestion of Forsyth Major that 
there was the possibility that the Rodentia may have been derived 
from the Multituberculata, even though the teeth of the Dogs 
could not be so derived. I was led to do this mainly for two 
reasons :—(1) the similarity between the dentitions of the Multi- 
tuberculata and the Rodentia; and (2) the valve of the Paleonto- 
logical evidence collected by Dr. Forsyth Major and published 
by him in numerous papers. It was therefore with the object of 
testing the validity of this suggestion from the embryological 
standpoint, that I commenced this research, the results of which 
are here set forth. 
The selection of Cavia as an animal upon which to work was 
chiefly due to the fact that my friend Mr. Martin F. Woodward 
had very kindly given me a series of foetal Guinea-pigs. Upon 
this material ready to hand, I commenced the investigation. I 
have also examined specimens of feetal rats, mice, and rabbits 
(with which I hope to deal more particularly in the future). These, 
though showing differences in detail, nevertheless appear to me 
* From the Morphological Laboratory, Cambridge. 
LINN. JOURN. —ZOOLOGY, VOL. XXVIII. Da 
