432 MONTGOMERY. [Vol. XIII. 



in others homogeneous. A priori we would expect the axis 

 cylinder, as any other organ, to be more highly differentiated 

 in the higher forms than in the lower; and the facts would seem 

 to be, indeed, that in some of the invertebrates it is homoge- 

 neous, while in the (higher) vertebrates it may be fibrillar. 

 And at any rate it is always unsafe to conclude that if the axis 

 cylinder, or any other nerve element, has a particular structure 

 in one organism, the same structure must exist also in but 

 distantly related forms. 



WiSTAR Institute of Anatomy and Biology, 

 Philadelphia, May 26, 1896. 



