(120 Dr. A. Ariibilck-CIiristie-Liiide o/i the 



functional lower incisors bolong to the permanent dentition. 

 This fact seems to justify the conclusion that also the first 

 pair of upper incisors belong to the same dentition. 



In this specimen Id', which was absent in the stages 

 described above of Crocidura 7-ussula, is present in the upper 

 jaw. 



Remits. 



The chief facts ascertained by my investigation, illustrating 

 the descent of the Soricidse and their relation to the other 

 Tnsectivores, are the following : — 



1. The presence of more than three incisor-gerras in botli 



jaws of Sore.v araneus, and probably also in the upper 

 jaw of Neoniys. 



2. The presence of a tooth-rudiment belonging to the 



milk-dentition situated between the upper P* and M^ in 

 Crocidura russula. 



3. The presence of other riulimcntary antemolars, proviiii^- 



that the Soricidie once had a full set of permanent 

 teeth. 



4. The presence of a rudimentary milk-dentition in the three 



genera Sorex, Neomys, and Crocidura. 



The germs of P and I- in the upper jaw and that of Ii in 

 the lower jaw are to be regarded as rudimentary organs 

 without any function. They are present in foetal specimens, 

 aiul disappear afterwards without attaining full development. 

 They are undoubtedly inherited from distant ancestors, 

 ivhich consequently ivere to be found among pohjprotudunt {and 

 heterodont) mammals. 



As is well known, the Mesozoic Mammalia — I think 

 especially of the Tritubercnlata, Osborn, which are regarded 

 by Osborn and several other zoologists as the ancestors of 

 the Insectivores — were characterized by polyprotodonty and 

 heterodonty. Yet no certain form among them can bo 

 pointed to as progenitor of the Soricida\ So far as I know, 

 no intermediate forms iiaxe been found between the Sorioidir, 

 with their enormously developed anterior incisors and their 

 want of canines, and the Mesozoic mammals, with their but 

 little specialized incisors and their highly differentiated 

 canines. But this may be due to the fact that the fossil 

 finds of INIesozoie mammals arc very few in number and 

 consist only of incomplete fragments. Several lower jaws 



