122 Journal of Comparative Neurology 



with the fact that in the olfactory region, in higher types — i. e. 

 the region in which the terminal filaments from the olfactory 

 bulb are distributed — the epithelium cells are columnar and non- 

 ciliated (Ref. Handbk Med. Sciences, Lit. No. 28.) while 

 in the respiratory portion of the nasal cavity the epithelium is 

 columnar and ciliated. 



The Dipnoi are the lowest types in which the nasal cavity 

 begins to differentiate for the secondary function of a respiratory 

 passage, from this stage onward the olfactory sac being in com- 

 munication with the mouth. 



4. Psycho-genetic conclusions regarding the sense of smell. 

 This is an apparently unworked field. Such questions as the 

 relation of the nasal apparatus to the habits of the animal ; the 

 psychogenesis of smell, etc., have but lately received any at- 

 tention deserving notice. 



Edinger' s flsychogenetic conclusions. — Although the olfactory 

 sac is developed by invagination of the ectoderm, and hence the 

 olfactory organ is developed later than the numerous tactile or- 

 gans scattered over the whole epidermis, yet the sense of smell 

 seems to be developed before the sense of touch. We must 

 not regard those reflexes which are seen in the motions of the 

 amoeba and other low forms as indicating the possession of any 

 true sense of touch, but only a susceptibility to stimulus, that 

 is, mere irritability. Thus we see that although the organs of 

 touch precede in development the organs of smell, yet because 

 the latter form their central connection first, the sense corres- 

 ponding is the first to be developed. That is, we may say that 

 touch and smell existed, and touch existed before smell, but the 

 sense of smell was the first to become conscious. (Properly 

 speaking of course, the sense of smell or touch is not rightly ' 

 called a sense until it becomes conscious.) Now the psychical 

 processes which pertain to the sense of smell have been referred 

 to (i. e. have their center in) the hippocampus. And if it is 

 true as seems almost certain that the Ammon's horn which is the 

 homologue of the hippocampus in lower types, is the first cor- 

 tical center to develop, then it would seem to follow that the 

 first psychical function to develop, corresponding to this most 



