XXX Journal of Comparative Neurology. 



of the careful descriptive work done in this field has been surprisingly 

 barren of morphological fruit. This is no doubt largely due to the 

 fact suggested by Professor Fish that the older methods are ill adapted 

 to differentiate the histological elements of these primitive brains. It 

 is a matter of familiar observation that methods well adapted to bring 

 out the details of a mammalian, reptilian or fish brain may leave the 

 amphibian tissue apparently a structureless mass of white and grey 

 matter. It is gratifying, therefore, to observe that this field is now 

 being assiduously cultivated by the aid of newer methods which promise 

 better things for the future. 



That the amphibian brain is the most primitive or generalized 

 type among the Craniota has been maintained by several of our ablest 

 neurologists on the basis of general form and topography. That the 

 same would prove true of the histological structure has long been 

 suspected but the lack of acurate knowledge of the details of cellular 

 structure and fibrous distribution has prevented safe generalization. 

 This of course applies to the Urodela more especially, rather than to 

 the Anura, where considerable diversity of structure has already been 

 demonstrated. Professor Fish's careful description of the cellular and 

 fibrous elements of Desmognathus as demontrated by the methods of 

 Golgi and Weigert will be a valuable aid in all future morphological 

 work. He considers the unipolar cells lying next to the endyma to 

 be the primitive type of neuroblastic element and that the processes 

 are exclusively cellifugal. One fibre of finer caliber than the others 

 of the dendridic mass separates from the latter as the neurite or axis- 

 cylinder process. Farther towards the periphery this neurite arises 

 from the very base of the dendridic process or from the cell body, 

 while the most peripheral cells are distinctly bipolar, the neurite and 

 the dendrite being at opposite ends. It is conceivable, we may add, 

 that this arrangement is correlated with the diffuse distribution of the 

 cellular elements and the relatively feeble development of the longi- 

 tudinal fibre systems, the functions of the latter being perhaps largely 

 carried on by the diffuse dendridic reticulum constituting the greater 

 part of the white matter. In order that cellipetal impulses may pass 

 from the white matter to the cells lying next the endyma the dendrites 

 of the latter must be directed peripherally through the outer layers of 

 nerve cells. As the cellifugal neurite must pass in the same direc- 

 tion, it is quite natural they should pass out together for part of their 

 course, forming a neurodendrite. Although Professor Fish decides 

 against this view, I see no reason why we may not assume that the 

 dendrites are cellipetal here, as in other cases. When, however, such 



