14 FRANK B. BEDDARD 



in time of origin to the germ of the persisting tooth of the adult 

 which arises from the end of the dental lamina. If this were 

 proved to be the case the homologies of both would need 

 another view than that put forward here. The actual time 

 at which the end of the dental lamina becomes the rudiment 

 of a tooth is hard to decide. 



In the memoir of Messrs. Pouchet and Beauregard the authors 

 figure ^ six sections of teeth, of which one only (Text-fig. 6) 

 represents a tooth of the lower jaw. All of the figures are 

 approximately alike, and an inspection of these drawings does 

 not lead to any possibility of distinguishing between the teeth 

 of the two jaws in this cetacean, or at any rate in an embryo 

 of 30 cm. in length. I have already mentioned the fact that 

 I was only able to discover anything that looked definitely 

 like a residual lamina in the teeth of the lower jaw in my younger 

 embryo. Nor do the figures of Pouchet and Beauregard (4) 

 show anything similar beyond all doubt to the projection of 

 enamel tissue which I have figured (see Text-fig. 4) to the 

 labial side of the undoubted tooth rudiment. There is, however, 

 in the former figures a thick process, forming really part of the 

 terminal expansion of the dental lamina, to be seen ; but it 

 will be noted that this is on the lingual side. The process does 

 not seem to me to be distinctive enough to set it down as 

 a residual lamina, even without going into the question of its 

 position with regard to the main ingrowth of the dental lamina. 

 And in any case those authors complain of the condition of their 

 specimen, which would render it unwise to do more than call 

 attention to such characters as are obviously not masked by 

 the inferior histological state of this specimen. 



In my younger example there was nothing that could be 

 compared to this residual lamina (if it be so) which is figured 

 by Pouchet and Beauregard. 



This, however, may easily be due to the fact that the state 



^ On PI. vii of the memoir already quoted. I may eall attention to the 

 slight confusion in the description of Pis. vii and viii : the former is stated 

 to be of an embryo of 1-30 m., the latter one of 0-30 m. Tlie reverse is 

 obviously the case. 



