764 I^r. J. BEARD, 



These cells are the foundation or Anlage of the olfactory neural 

 ganglion. A slightly later stage is shown in fig, 14. 



Some of those on the right-hand side are still partially connected 

 with the epiblast. The cells are also beginning to grow down towards 

 the olfactory neuroepithelium, and in the next stage figured they lie in 

 close connection with the latter, and in some places are fused with it 

 (fig. 12). 



The fore brain has closed in, and there are no longer any of the 

 cells of the ganglionic foundation on its summit. 



The development of the olfactory epithelium will now be taken 

 up, and we shall follow the formation from it of the nose proper and 

 Jacobson's organ. In the figure just examined (fig. 12), which is 

 taken from a very young embryo of L. agilis — a stage very much 

 younger than M. Béraneck's stage IV, — one notices that the ol- 

 factory neuro-epitheliura is represented by a simple epiblastic thicken- 

 ing, which has as yet undergone no invagination at all. The limits 

 of the neuro-epithelium are very sharply marked ofi' from the indifferent 

 epiblast above and below, or neurally and haemally. In fact, at this 

 stage the neuro-epithelium diff'ers in no characteristic from the neuro- 

 epithelium connected with a typical branchial nerve such as the glosso- 

 pharyngeus. 



In the latter case the neuro-epithelium gives rise in fishes to 

 branchial or lateral sense organs, and even in Reptiles these typical 

 branchial nerves, such as the facialis and glossopharyngeus , possess 

 well-developed neuro-epithelia above the gill-clefts in certain stages. 



From researches I have not yet published, the neuro-epithelia of 

 facialis and glossopharyngeus in Reptiles (at least) appear to give 

 rise to the taste buds of the mouth. 



The piece of olfactory neuro-epithelium in the lizard soon begins 

 to undergo a series of changes. For a long time during the deve- 

 lopment rapid cell-divisions take place within it. These cell-divisions 

 give rise, as we shall see, to the sensory end-cells and several 

 layers of ganglion cells. 



The neuro - epithelium also begins to invaginate, but unlike the 

 case of Elasmobranchs , the invagination almost from the start is not 

 a simple one. It takes place in such a way as to divide the neuro- 

 epithelium into two small depressions or pockets (figs. 25 and 26 p. 766). 



1) In this group these structures were first seen by Béraneck. 



