Morphological Studies. 769 



in the section , and the figure depicts a section taken through the 

 central portion of Jacobson's organ. 



The columns of smell-bud ganglia have increased in size, and 

 project into the mucosa more than in the last figure described. They 

 appear to have increased at the cost of the cells forming the outer 

 layer of „nuclei" in fig. 6, 



Here, as during the whole course of development, it is very easy 

 to demonstrate that the fibres of the olfactory nerve end in these co- 

 lumns, or smell bud ganglia (see figs. 4 and 5). 



Jacobson's organ of the adult snake. 



In a section of Jacobson's organ of an adult snake, such as is 

 figured in fig. 7, it will be noticed that the smell -bud ganglia are 

 still more marked than in the embryo, and indeed, the whole sensory 

 epithelium of Jacobson's organ is split up into a number of columns. 

 Towards the free surface of the organ each column forms a smell-bud 

 comparable to those described by Blaue in Teleosteans and Amphi- 

 bians (38). The base of each smell-bud is made up of a long column 

 of ganglionic cells, which in its turn receives the fibres of the olfac- 

 torius at its base. 



The figure of the adult organ (fig. 7) is not as good as I could 

 have wished it to be. Unfortunately, at the time this subject was under 

 investigation, only spirit specimens of adult snakes could be obtained. 

 The state of histological preservation of the specimen used was not 

 very bad, and I have been obliged to content myself with what 

 could be got from it. 



I have represented a few of the sensory cells of Jacobson'« 

 organ from one adult, and also their connection, so far as it could 

 be made out, with the lower lying „nuclei" (fig. 3). 



The figure is sufficiently good to show the close agreement in 

 minute structure between the sensory epithelia of Jacobson's organ 

 in the snake and in the guinea-pig {Cavia) as depicted by Dr. Klein 

 (17, PI. VII, figs. Ill and IV). 



It was not likely that the striking appearance of Jacobson's 

 organ in the Ophidia, as described above, should have hitherto escaped 

 notice, although nothing is said of the matter in the text-books. 



Leydig (23, p. 324, PL XV, figs. 5, 6 and 7) had already seen 

 — and indeed, what has he not seen? — these columns of ganglion 

 cells in the year 1872, but the methods employed by him were not 



