Literary Notices. clxiii 



plate. The question is open how far the embryonic character of the 

 ependyma is primitive and how far reductive. Goronowitsch argues 

 for the degenerative nature of the pallium of fishes. This is debat- 

 able. Burckhardt considers it more probable that the brain of ganoids 

 has given rise to that of teleosts by the lateral extension of the ver- 

 tical plate, crowding the lateral zones to one side just as has been 

 done in the roof of the fourth ventricle. Since histologically the me- 

 dian zones are the most primitive, we should expect that they would 

 show also the smallest amount of morphological deviation in the var- 

 ious types. Such in fact is found to be the case. 



Now follows a detailed description of the median zones in the 

 different types of vertebrates, which could not be well abstracted 

 without a reproduction of the plate which accompanies it. In this 

 plate are represented the median sections of ten typical vertebrates 

 from Amphioxus to man, so drawn by means of an ingenious color 

 scheme that the homologous segments of the median zones appeal to 

 the eye at once. The result is very impressive. The amount of vari- 

 ation is found to be surprisingly small. This plate will be useful to 

 teachers for the purpose of demonstration to classes in comparative 

 anatomy. 



The causes which produce modification in the structural plan are 

 briefly discussed and also the phylogenetic relationships. The brain 

 of Notidanus is regarded as a primitive type. As to the lines of 

 differentiation, the following points are suggestive: — The more primi- 

 itive the brain, the more uniform the thickness of the lateral zones, 

 the less they influence the median zones and the less the brain axis is 

 deformed. Increase of mass is of less importance than diversity of 

 form. This specialization will take different paths. The teleosts rep- 

 resent a culmination ; so do the birds, mammals, and among the latter 

 the microsmic mammals. In the median zones resides the conserva- 

 tive element; in the lateral zones, the progressive element. The one 

 gives us the structural plan ; the other its modifications. 



Though the papers above noted are written from different stand- 

 points and show great diversity as to both methods and conclusions, 

 yet the careful reader can hardly fail to be struck by the fact that, after 

 all, the agreements are of greater importance than the differences 

 Much permanent gain will certainly result from so careful a sifting of 

 the facts by these eminently careful investigators. 



C. J. H. 



