cxxxviii Journal of Comparative Neurology. 



and remains enclosed within the latter. These changes take place sub- 

 stantially cotemporaneously throughout the peripheral end. A secondary 

 fragmentation occurs first in the vicinity of the nuclei. By the seventh 

 day there is active proliferation of the nuclei. After subdivision the nu- 

 clei migrate and set up new centres of absorption. 



Regeneration begins with the formation of new protoplasm about the 

 nuclei, which then assume the form of bipolar cells ; at a later period the 

 whole sheath is filled with a continuous belt of protoplasm in which the 

 nuclei are imbedded. Such a fibre is called an embryonic fibre by reason 

 of its resemblance to the early condition. In some cases it appears that 

 two new fibres may be formed in one old sheath. 



In case the cut ends are not united, regeneration never gets beyond 

 the embryonic stage. If united the myelin is formed discontinuously, 

 generally near the nucleus, subsequently uniting to form a continuous 

 sheath. Respecting the nuclei, the authors are not clear. They suppose 

 that they disappear by absorption. 



"With reference to the nodes and internodes of Ranvier, it is evi- 

 dent that no sim]5le hypothesis, such as the development of each inter- 

 node from a single cell, will fit the facts as they appear in regenerating 

 fibres." They admit that the internodal nucleus must, throughout life, 

 play an important part in the nutrition of the protoplasm in connection 

 with it and of the myelin sheath. " In an indefinite way we may sup- 

 pose that this nutritive influence on the myeline can only extend over a 

 limited area — the distance of an internode, —but to connect this with the 

 formation of these internodes takes us into the field of speculation, 

 though it seems to us that the true explanation lies along this line of 

 thought. The origin of the segments of Lantermann may doubtless be 

 traced directly to the primitive, disconnected deposits of myeline which 

 we have described." The authors seem to believe that the axis cylinder 

 proceeds from the slump into the newly formed myelin, a position ren" 

 dered very improbable by their figures. 



" In the central end, especially when connection with the periphery 

 is not made, several new fibres may form within the sheath of an old one 

 to take the place of the portion degenerated. Each of these may de- 

 velop myeline and receive a branch from the axis cylinder above." 



The paper is a credit to American science and it is a great pity that 

 it should not have found an American medium of puljlication. The 

 plates are exceedingly instructive. 



