772 ^^- '^- BEARD, 



columns, though not so marked as in the Ophidia, is, however, to be 

 made out more or less perfectly in both Lacerta and Anguis (figs. 

 9 and 10). But, except in the Amphisbaenidae, it has not yet been 

 possible to detect a division of the sensory end-cells into smell buds 

 such as can be observed in the adult snake (figs. 7 and 15). 



Jacolbson's organ and the ordinary nasal epithelium 

 in Ophidia and Lacertilia. 



I have not had any good sections of the nasal epithelium of 

 adult snakes, but in sections through advanced embryos of the stage 

 represented in fig. 6 for Jacobson's organ, it is not difficult to make 

 out the same regular wavy outline as in Jacobson's organ of the 

 lizards. I have represented an exact camera drawing of such 

 a piece of olfactory epithehum from the same embryo as fig. 6 in 

 fig. 13. Here it is very obvious that similar divisions into smell-buds 

 and their ganglia are at the bottom of the structure of the nose, as 

 well as of Jacobson's organ, in snakes. The difference lies in the 

 lesser development of the smell-bud ganglia in the former case, and 

 Jacobson's organ in snakes (for that matter in Lacertilia also), must 

 be an incomparably finer sense organ than their nose- 

 proper. 



Anguis and Lacerta have essentially the same sort of nasal epi- 

 thelium as Tropidonotus. That is, they, and to a still gi-eater extent 

 the Amphisbaenidae, present the appearances in their olfactory epi- 

 thelium which have just been described for Ophidia, and fig. 13 would 

 sei-ve for the former just as well as for the latter. I have not thought 

 it worth while to figure the olfactory epithelium of either Lacerta, or 

 Anguis^ or an Amphisbaenid. 



Conclusions. 



It was almost certain before these researches, and it is now a 

 fact, that Jacobson's organ of Keptiles is a specially diflerentiated 

 part of the nose. It is most highly developed in Lacertilia and Ophi- 

 dia, and as yet no trace of it has been found in either Crocodilia or 

 Chelonia. I have searched for it in Chelonians and in embryo Cro- 

 codiles, but in vain. 



The two groups in which Jacobson's organ is well developed, 



