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Mr. W. H. Flower 07i the Development 



[May 9, 



The following communications were read : — 



I. On the Development and Succession of the Teeth in the Mar- 

 supialia.'^ By William Henry Flower, F.R.S., F.R.C.S., 

 &C.5 Conservator of the Museum of the Royal College of Sur- 

 geons of England. 



(Abstract.) 



Although the dentition of adult individuals of all the animals which con- 

 stitute the remarkable Order or, rather. Subclass Marsupialia, has been 

 repeatedly subjected to examination, and described with exhaustive minute- 

 ness of detail, it is a singular circumstance that most of those peculiarities 

 in the succession of their teeth which distinguish them from other mammals 

 appear hitherto to have escaped observation. To supply this blank is the 

 object of the present communication. Fortunately the materials at my 

 disposal, although not quite so complete as might be desired, are yet 

 amply sufficient to illustrate the main aspects of the question, and to 

 supply a result as interesting as it was unexpected. 



Descriptions are given in the paper, accompanied by drawings, of several 

 stages of the dentition of members of each of the six natural families into 

 which the order is divided. 



1. Macropodidce. — The dentition of the Kangaroo (genus Macropus), 

 from the completely edentulous foetus to adult age, is described in detail. 

 Contrary to what has been specially stated with regard to this genus, there 

 are no deciduous or milk-incisors, the teeth of this group which are first 

 formed and calcified in both jaws being those which are retained throughout 

 the life of the animal. The rudimentary canine and first premolar have 

 also no deciduous predecessors. The second tooth of the molar series (a true 

 molar in form) is vertically displaced by a premolar. The four true molars 

 have, as has long been known, no deciduous predecessors. There is thus 

 but one tooth on each side of each jaw in which the phenomenon of diphyo- 

 dont succession occurs. The period at which this takes place varies in 

 different species of the family. In some forms oi Hypsiprymnus, the suc- 

 cessional premolar is not cut until after the last true molar is in place and 

 use, — this probably having relation to the extraordinary size of the tooth, 

 and the time consequently required for its development. A special charac- 

 teristic of this family is the tendency to lose the canine and one or both 

 premolars at a comparatively early period of life. 



.2. Phalangistidce. — Several early stages of the dentition of Phalangista 

 vulpina are described and figured. In a young specimen in which no teeth 

 had cut the gum, the crowns of the permanent incisors, canine, and first 

 two molars were found to be calcified, and the germ of the permanent pre- 

 molar was already formed beneath the milk- or deciduous molar, which, as 

 in Macropus, is the only tooth which is shed and replaced by a successor. 

 The change takes place at an earlier period than in the last family. 



3. Peramelidee. — No very early stages of Permneles were examined ; but 



