1 6 Journal of Comparative Neurology and Psychology. 



those fibers which are nearly circular, in which the sheath is 

 single and where there has been no increase in sheath from 

 careless printing, the measurements show the same relations 

 which we obtained on the specimens themselv^es. 



We feel justified, therefore, in making the broad statement 

 that in the peripheral nerves of vertebrates above the Cyclo- 

 stomes, we have in general a one to one relationship existing 

 between the nerve sheath and the axis, whether we compare 

 the volumes of the two or measure their areas in the cross sec- 

 tions of osmic acid specimens. It is to be anticipated, how- 

 ever, that somewhere among the fish we shall find examples of 

 less complete development of this sheath, thus bridging the gap 

 between the condition here found and that represented by the 

 nerves of Cyclostomi and Acrania which are without the me- 

 dullary covering. 



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