of the Tooth-Rudiments in Rodents. 307 



such an investigation seems at tlie veiy outset to offer but few 

 prospects of success. 



Tiie material investigated by me is derived from embryos 

 of Lepus cum'culus, Sciurus vulgaris, Gavia cobaya, Gncetus 

 frumentariusj Mus decumanus, and Mus musculus. My 

 methods consisted in the preparation of continuous series of 

 sections througli the lieads of embryos according to well-known 

 precepts. In particular I made use of the technique intro- 

 duced by Prof. Born in the Breslau Anatomical Institute, as 

 described by himself in his paper entitled " Noch einmal die 

 Plattenmodellirmethode " *. 



Plate-models were prepared of the most important stages. 

 These naturally contained the epithelial tooth-rudiments, as 

 well as the epitlielium of the oral cavity from which tliey had 

 proceeded ; it is evident that Malin [loc. cit.) worked in a 

 precisely similar fashion. 



I will take first the two species in the investigation of 

 which positive results have been obtained, i. e. Lepus and 

 Sciurus. The remaining forms, in which, in the sense of the 

 queries which we have propounded, nothing was discovered, 

 can subsequently be dismissed in a few words. 



Lepus. 



With reference to this form a series of statements are con- 

 tained in Pouchet and Chabry's paper [loc. cit.), which it is 

 necessary for me to cite, since I have partly to confirm, partly 

 to amplify, and partly to refute them. The French authors 

 confirm the older observations, that in the premaxilla of the 

 Rabbit three larger incisors are formed on each side, which, 

 however, do not stand side by side, but one behind the other. 

 The second of the series are deciduous, and drop out shortly 

 before or shortly after birth. The i. Sf are formed much 



* Zeitsclu'ift fur wissenschaftlicbe Mikroskopie, Bd. v. : Braunschweig, 

 1888. In this paper Prof. Born writes as follows : — " As is well known, 

 the essence of the plate-model method is that from each of a series of 

 sections of equal thickness the parts which are to be modelled are drawn 

 upon plates, which are exactly so much thicker than the section as the 

 sketch is larger than the original. The parts drawn are cut out and stuck 

 one upon another ; in this manner a plastic reconstruction is obtained of 



the structure under investigation " (p. 445) " Formerly I scratched 



the outlines of the section upon prepared (cast) plates. I now use plates 

 of waxed paper, in accordance with Strasser's suggestion, and after 

 drawing upon the paper, I cause this to be thickened with wax until plate8 

 of the desired thickness aie obtained" (p. 446). 



t For convenience' sake here and subsequently di. 2 (according to the 

 customary nomenclature) is designated shortly i. 2, while the permanent 

 ?. 2 is termed i. 3. 



