190 Journal of Comparative Neurology. 



end-organs which are tendinous at both extremities and we have 

 observed the same fact in a few cases. 



In all the mammalia we have studied, we have found no 

 neuro-tendinous end-organs which were not encapsulated. 

 Ciaccio, however, mentions the peculiar fact that in the bat, he 

 finds the spindles in the anterior extremity non-encapsulated, 

 while those in the posterior extremity always possess a distinct 

 investing sheath. While we have observed no such marked 

 variation in the end-organs of the mammalia which we have 

 studied, we do find a marked difference in the thickness and 

 density of the capsule, it being at times so thin that our most 

 careful manipulations failed to preserve it intact ; at others, so 

 dense that it held the intrafusal tendon bundles in place in spite 

 of much more violent treatment. Cross sections also show a 

 marked difference in the thickness of the capsule, at times 

 showing only one or two layers of connective tissue fibers with 

 a few nuclei, at others, several layers arranged rather densely 

 around the spindle and surrounded by still other layers of looser 

 connective tissue. This variation was noticed, not only in dif- 

 ferent muscles of the same animal, as observed by Ciaccio, but 

 even in different parts of the same muscle. 



The capsule consists of from one to several layers of white 

 fibrous connective tissue, in which we have been unable to de- 

 monstrate any yellow elastic fibers, either by Unna's orcein 

 stain for elastic tissue or by the methylen-blue, which often 

 stains yellow elastic fibers a pale blue. Between the bundles 

 of white fibrous connective tissue in the capsule, are connective 

 tissue cells. Both Golgi and Cattaneo have demonstrated, by 

 means of silver nitrate, that this capsule is enveloped by a layer 

 of large polygonal endothelial cells. 



In the axial space, we find a varying number of tendon 

 fasciculi, the intrafusal tendons, which differ from ordinary ten- 

 don in having a greater number of nuclei, the fasciculi being 

 smaller, both nuclei and fasciculi staining more readily and more 

 intensely so that they are readily differentiated from the sur- 

 rounding tendon. We now and then find in certain regions of 

 the intrafusal tendon fasciculi what Kolliker has described as a 



