018 Dr. A. Aiiibuck-Cliristie-Liiule on (lie 



The supposition that the tooth-rudiment in question 

 would represent the predecessor of a suppressed premolar 

 involves the same consequence. 



But as yet nothing is knovrn of a mammal belonging to 

 the Cainozoic age with more than four premolars, and the 

 s ime number is also typical of the hypothetical ancestors of 

 the Iiisectivores. 



As thus the tooth-germ Mx can hardly be regarded as a 

 premolar, it must, of course, be a molar-rudiment. In tiie 

 following I will give further reasons for this view. 



The tooth-germ Mx has been found on both sides in the 

 upper jaw in both the examined specimens of stage I. 



In stage II. only Pd' remains, also the tooth-rudiment 

 M\ has vanished, but the tooth-band between P' and AP i^ 

 swollen. 



In stage III. all the tooth-rudiments have disappeared 

 except a few cells of Pd\ which remain on one side. 



Tlie lower jail'. 



Highly vestigial traces of Pdj, Pdo, and Pd^ are present iu 

 stage I. They are about to be absorbed. 



In stage II. there is a remainder of Pd^, but in stage III. 

 every trace of the milk-dentition has disappeared. Thus the 

 milk-teeth in both jaws do not calcify and are all absorbed 

 before birth. 



Sum77ia)'i/. 



1. The tootb-band is continuous in the upper jaw, though 



liighly reduced in the middle; it is divided into two 

 halves in the lower jaw, as in Neomys fodiens. 



2. There are no rudiments of suppressed upjier teeth in front 



of the large incisors ; in this Crocidura differs from 

 Sorex (and also probably from Neomijs) . 



3. I' — the functional third incisor — is retarded in its deve- 



lopment, and has lost its predecessor in the milk- 

 dentition. 



4. P^ is retarded in its development. 



5. The upper P- is present in the youngest stage, but has 



lost its predecessor in the milk-dentition. 



0. There are no definite traces of suppressed teeth in front 

 of the large incisors in the lower jaw. 



7. A vestigial trace of the lower P., lias been found. 



