202 Journal of Comparative Neurology. 



free in the frog, generally free but occasionally encapsulated in 

 the turtle, generally encapsulated but occasionally free in the 

 bird and always encapsulated in the mammal; that in the young 

 kitten, the [capsule is thinner and more imperfect than in the 

 adult cat and that end-organs taken from different parts of the 

 same body may differ in the thickness of the capsule ; and that, 

 whether free or encapsulated, the nerve invariably ends on ten- 

 don fasciculi having the same characteristics and differing in the 

 same way from ordinary tendon. There seems to be here a 

 gradual transition corresponding to the development of the an- 

 imal. We think it true also in general that those end-organs 

 which have the most perfect capsule are the most complex and 

 well developed as regards their nervous structure. Since end- 

 organs of different degrees of complexity of nerve endings are 

 often found in the same animal as well as of different degrees 

 of perfection of the capsular envelope, we can not agree with 

 Ciaccio that his finding is a logical argument against the idea 

 that the encapsulated neuro-tendinous end-organs of the higher 

 types of vertebrates are developed from the free endings in 

 the lower forms and that the capsule is one indication of that 

 development. 



Function. — All those who have investigated the neuro-ten- 

 dinous end-organs seem agreed that they are sensory in their 

 nature. The resemblance of general structure to that of other 

 known sensory organs, the fact that the nerve supplying this 

 organ resembles in character those supplying other sensory or- 

 gans and can often be traced from the same nerve bundle, and 

 still more conclusive, the fact that we have observed the same 

 nerve fiber supplying this organ which supplies a neuro-muscu- 

 lar spindle, proved sensory by Sherrington's physiological ex- 

 periments, all seem to make the conclusion fairly certain, 

 while, if any doubt remained, the experiments of Cattaneo, 

 showing the degeneration of the nerves and endings in the end- 

 organs, after section of the peripheral nerve trunk, while they 

 remained unaltered after section of the anterior roots, should 

 set them at rest. 



