Morphological Studies. 763 



As a matter of fact the development of the Vertebrate nervous 

 system is very intricate, and by no means so simple as hitherto 

 supposed. And I feel it my duty to point out that wc are only just 

 beginning to see how complex are the problems presented to us in 

 our attempts to solve the nature of the central nervous system. Some 

 of us fail to recognise this truth, otherwise no investigator would sit 

 down with a number of sections through the brain and nerve-roots 

 of man or the dog, and endeavour from these alone to reduce the 

 peripheral nervous system to a segmental arrangement. 



The development of the olfactory nerve and organ, and 

 Jacobson's organ in Reptilia. 



So far as I am aware, no-one has really investigated the develop- 

 ment of the olfactory nerve in the lizard or snake. Béraneck (2, 

 p. 526) has made certain statements on this head which are quite in- 

 correct. As an instance of his inaccuracies it may be mentioned 

 that he finds that the olfactory lobe develops first, and that long 

 afterwards the olfactory nerve makes its appearance. 



In his stage IV, which is the earliest described, the embryo 

 has all its other nerves well-developed, even its hind-limbs are pretty 

 far advanced, but although it has a small olfactory lobe it is without 

 olfactory nerve. Further, in his figure of this stage (pi. XXVIII, 

 fig. 1), the olfactory organ is already represented by a pit in the 

 epiblast. Under these circumstances no value can be attached to the 

 observations and assertions of M. Béraneck on the olfactory nerve 

 and organ in the lizard. 



On the development of Jacobson's organ in Reptiles we have 

 the observations of Born and Fleischer which have already been 

 quoted in the introduction to this paper. Béraneck says very little 

 about Jacobson's organ (2, p. 530). 



The earliest stage in which I have been able to find the found- 

 ations of the olfactory ganglion, — that is of those ganglionic cells 

 (neural ganglion) which give rise to the olfactory nerve, corresponds 

 exactly to fig. 22 {Torpedo) — the first stage described in Elasmo- 

 branchs. It is figured in fig. 11. Here as in figs. 22 and 24 the „ant- 

 erior neuropore" has not yet closed, and at its lips certain cells are 

 being proliferated from the epiblast, just as in sharks. 



