208 HANSFORD MacCURDY 



generated in three months, but a large number had disappeared 

 after nine months. Ranson ('06) observed no further change after 

 two months, and for this reason concluded that degeneration was 

 not progressive. In the present series of experiments some cells 

 had lost all distinguishable structures in twenty-one days, and a 

 greater number was found in this condition twenty-eight to thirty- 

 nine days after the injury. It is, therefore, reasonable to believe 

 that degeneration takes place slowly in some cases and more 

 rapidly in others. These differences are best explained by the 

 differences in the animals used and in the nature and the condi- 

 tions of the experiments. 



The results of this series of experiments furnish some additional 

 support to the view that the continued life of the neurone depends 

 upon the performance of the normal functions of all its parts. 



SUMMARY 



1. Observable structural changes occur in many of the gan- 

 glion cells of the fifth abdominal ganglia of Cambarus three to 

 seven days after the connectives are severed between the fourth 

 and fifth, and the fifth and sixth ganglia. 



2. A smaller number of ganglion cells in the fourth and sixth 

 ganglia likewise degenerate. 



3. Complete degeneration of many of the cells occurred twenty 

 eight to thirty-nine days after the nerve fibers were severed. The 

 length of time required for degeneration varies. 



4. The histological changes accompanying degeneration in 

 these nerve fibers and nerve cells are similar to those which have 

 been described by others for the nerve fibers and nerve cells of 

 vertebrates, excepting those w T hich pertain to the medullary 

 sheath, which is absent in Cambarus. 



Accepted by the Wistar Institute of Anatom3 - and Biology, April 17, 1910. Printed July S, 1910. 



