262 DR. H. W. MARETT TIMS ON 
to confirm the conclusions upon the broader issues with which I 
am here mainly concerned. If my identification of the individual 
teeth in Cavia be correct, it then follows that the identification 
usually accepted of the teeth of the Rodents in general may in 
many instances be incorrect. This being sc, 1 have deemed it 
advisable to limit myself, in the present instance, to the teeth of 
the Caviide, and not to deal with the Order as a whole as was 
originally my intention. 
The method I have followed has been that of cutting and 
examining serial transverse sections of the jaws, after staining in 
bulk. In some cases the stain used has been borax-carmine; in 
others Tomes’s ferric-perchloride and tannic-acid method was 
adopted. The jaws were decalcified in a 2 per cent. solution of 
each of the following, viz.:—hydrochloric acid, nitric acid, and 
ferric perchloride. The object in using a combination of the two 
acids being to neutralize the shrinkage of the tissues caused by 
the former by the swelling caused by the latter. After decalci- 
fication, the iron in the tissues was reduced by a 38 per cent. 
solution of tannic acid. Wax models of the younger stages of 
the teeth have been made, while in the older the teeth were 
examined in situ by clarifying the jaws in oil of cloves. 
I shall commence with a detailed description of each stage, 
comparing my results in each case with those of other writers, 
and will leave a general consideration of the problems involved 
to be dealt with in the latter part of the paper. 
CAVIA COBAYA. 
Stage 1. Circumferential head-length... .. 15 em. 
body-length ... 4cm. 
Fig. 1. 
ann A 
pe 
Reconstructed diagram, showing the number and position of teeth present in 
Stage 1. pi., permanent incisor; dm., deciduous molar ; m!, first molar. 
In this, the youngest stage examined, rudiments of three teeth 
were to be found in the upper jaw, none, however, showing any 
traces of calcification. The three teeth present are the incisor, 
