274: DR. H. W. MARETT TIMS ON 
disappeared even though the teeth had not cut the gum. This 
confirms the observation made by Saint-Loup [18], which led 
him to ask the question whether this is a case of the hereditary 
transmission of acquired characters, since it cannot be due to 
wear. 
The posterior tooth is much smaller; its characters I was not 
able definitely to ascertain owing to its position and the difficulty 
of dissecting it out from its osseous surroundings. 
The surface view of the deciduous tooth is seen in outline in 
fig. 5B; a comparison of this with the teeth shown in Pl. 26. 
fies. 7 & 8 is, I think, suggestive, the same general pattern 
being noticeable: more particularly is this the case on com- 
parison with the tooth of Stichomys of the Lower Eocene; the 
latter is, however, slightly more complicated. This fact may 
afford some additional argument in favour of the multituber- 
culate origin of the Rodent molars. 
Stage 5 (Post partum). Circumferential head-length 5 cm. 
2 body-length 12 cm. 
Fig. 6. 
19 OV ON 
A. View of teeth in Left Upper Jaw (Stage 5), seen from outer side. 
B. Crown-surface of permanent premolar and three molar teeth. 
Examination of the clarified jaw shows the presence of four 
cheek-teeth only, all traces of the deciduous molar having dis- 
appeared. Of these teeth the second is the largest, and is the 
only one in addition to the incisor which has actually cut the 
gum. AJ] have assumed the characteristics of the adult denti- 
tion. The enamel is absent from the crown-surfaces, all trace 
of definite cusps bemg wanting. A side view of the teeth 
situ is shown in fig. 6 A, while the crushing surfaces are repre- 
sented in fig. 6 B. 
