292 Dr. W. Kiikeiitli:il o„ the 



3 and 3'2 centim. fioiii nnni) to nape. The ej)itlielial cofJ.s 

 and their knobbed swellings are traceable with the utmost 

 distinctness on the inside of the dental rudiments {vide 

 figs. 2-7). 



We now come to the interpretation of the facts observed. 

 In all three larger stages we see the dental rudiments dis- 

 tinctly developed, and moreover an epithelial cord running 

 close to and on the inside of them, which arises from the neck 

 of the enamel-organ and is provided with a swollen free end. 

 In these lateral cords of epithelium we have before us 

 PERFECTLY TYPICAL RUDIMENTS OF THE EARLIEST STAGES OF 

 THE ENAMEL-ORGANS OF SUCCESSIONAL TEETH, and they are 

 indicated with special distinctness in the case of the whole of 

 tlie incisors j remains of these rudiments are also seen in the 

 case of the canine as well as in that of the first molar, and it 

 was only in the case of the second premolar that I did not 

 succeed in discovering them. A valuable subject for com- 

 parison is furnished by the third premolar, to which a succes- 

 sional tooth actually a])pears later on. Now the rudiment of 

 the enamel-organ of its successional tooth agrees so entirely 

 with that of the rudiments of the other successional teeth that 

 there is nothing to prevent their homologization. The dis- 

 covery of rudiments of successional teeth in the case of teeth 

 other than the third premolar, which Thomas himself declared 

 would be fatal to his hypothesis, has therefore been achieved, 

 and moreover not in the case of one, but in that of almost all 

 teeth. It is for the present a matter of indifference to us 

 whether these enamel-organs of the rudiments of successional 

 teeth undergo still further development or become rudimentary 

 at an early period ; in any case the nature of the dentition of 

 Dideli)hys^ZiX\(\.^ as I shall immediately add, in all probability 

 that also of the rest of the Marsupials, is settled. The 

 PERMANENT DENTITION OF THE MARSUPIALS BELONGS TO THE 

 FIRST SERIES, THE MILK-DENTITION; RUDIMENTS OF THE 

 SECOND DENTITION ARE ACTUALLY PRESENT IN AN EMBRYONIC 

 CONDITION, BUT WITH THE EXCEPTION OF THE THIRD PRE- 

 MOLAR IT DOES NOT CUT THE GUM. 



A fevv words yet remain to be added as to the rudiments 

 of the so-called true molars, the molars. The smallest stage, 

 1 centim. in length, showed as yet no trace of a rudiment 

 either in the upper or in the lower jaw. It was only in the 

 three subsequent larger stages that rudiments of these teeth 

 could be detected, and here they were nearly equally far 

 advanced in development. In the upper jaw the first and 

 second molars were present, in the lower jaw the first, second, 

 and third. In all lases development was already far advanced j 



