1865.] The Development of Nerve-fibres. 263 



tion and disappear, in fact the nuclei may live and increase at its expense, 

 and a new mass, consisting entirely of nuclei, or masses of germinal matter, 

 by the agency of which .the formed material of the new fibres is at length 

 produced, may result ; but never does old tissue split up into new tissue. 



As I have pointed out on many occasions, in fully-formed organs there 

 exists a certain proportion of embryonic germinal matter, which may un- 

 dergo development at a future period of life, and if the greater part of this 

 becomes fully-formed tissue, still there remains embryonic matter for de- 

 velopment at a still later period, and so on. In the situations of these so- 

 called nerve-tufts in the breast-muscle of the frog, new elementary muscular 

 fibres are added to those already formed, and the muscle grows as the frog 

 advances in age. In the formation and growth of the muscular fibres, and 

 in the formation and arrangement of the nerves around them, the move- 

 ments of the several nuclei or masses of germinal matter to which I have 

 drawn attention, play no unimportant part. (See my paper " On the 

 movements of the living or germinal matter of the tissues of man and the 

 higher animals," Archives, vol. iv. p. 150.) 



With reference to the nerves supplying these so-called nerve-tufts, I 

 would remark 



1. That two dark-bordered nerve-fibres, running in the same sheath, 

 may often be traced to one part of the " nerve-tuft." 



2. Besides the dark-bordered fibre or fibres, there are invariably very 

 fine fibres running in the same sheath. 



3. That the dark-bordered fibres and the accompanying fine fibres 

 divide and subdivide very freely amongst the young muscular fibres, and 

 that thus quite a leash of very fine nerve-fibres results, in the course of 

 which numerous nuclei exist at certain intervals. Many of these can be 

 followed upon or between the muscular fibres, for the distance of the 

 twentieth of an inch or more from the oval swelling. These points are 

 well seen in the figures to which I now direct attention. 



4. That the dark-bordered fibre or fibres which enter at the tuft are not 

 the only nerve-fibres distributed to these bundles of muscular fibres, but 

 that invariably a bundle, consisting of two or three fine but dark-bordered 

 fibres, is connected with the muscular fibres, at a point above or below 

 that at which the swelling is situated, where the large fibre or fibres enter. 

 Sometimes there are two such bundles, one above and one below. These 

 not unfrequently give off branches, just before they pass to the muscular 

 bundle, which pursue a longer course, and are distributed to other larger 

 muscular fibres ; and oftentimes branches pass from one muscular bundle to 

 more distant ones. 



From the above observations it follows that these "nerve-tufts" in the 

 breast-muscle of the frog consist of developing muscular fibres, which are 

 freely supplied with nerves ; and the number and distribution of the nerves 

 render it probable, not only that there are entering and emerging fibres, 

 nerve-loops, and plexuses, or networks, upon the muscular fibres, rather 



