262 Dr. Beale Croonian Lecture. [May 11, 



fibres. These may be followed for a considerable distance amongst the 

 developing muscular fibres. 



It has been truly stated by Kolliker that the apparently single muscular 

 fibre bearing the swelling is really a bundle of very fine muscular fibres, 

 varying from three to seven, or more, in number, and that the apparently 

 penetrating nerve-fibres merely pass between these imperfectly developed 

 muscular fibres. I cannot, however, agree with him in the view that the 

 fine muscular fibres result from longitudinal splitting of wider fibres. The 

 bundles of fine muscular fibres under consideration extend, it is true, at a 

 certain period of their development, from one extremity of the muscle to 

 the other ; but all the muscular fibres of the bundle do not reach so far. 

 In one bundle sometimes ten or twelve distinct muscular fibres, very closely 

 packed together, may be counted. Near the swelling the muscular fibres 

 are wide, and the fine, tapering, pointed extremities of other young mus- 

 cular fibres can also be seen. These spindle-shaped muscular fibres are 

 not nearly so long as the ordinary fully developed muscular fibres. In 

 fact, at the swelling, several spindle-shaped, nucleated, already transversely 

 striated muscular fibres may be observed, and the stages through which 

 the elementary fibres of voluntary muscle pass in their development may 

 be traced. 



In these "nerve-tufts " we may indeed study, in the fully-formed animal, 

 striped muscle and nerve in every stage of development. Vessels cannot 

 be traced into the youngest tufts ; but in those which consist of several 

 partly grown muscular fibres, capillaries are to be seen ; so that the develop- 

 ment of muscles, nerves, and vessels can be studied in these imperfectly 

 developed "tufts." 



From the above observations, it will be seen that I cannot agree with 

 Kolliker in the view he has taken of these bodies. He says, " Now if it 

 be admitted that the finer muscular fibres composing the bundle are gene- 

 rated by the division of thicker muscular fibres, as Weismann justly con- 

 cludes, the explanation of the nerve-tufts becomes easy, inasmuch as they 

 may be conceived to arise from a simultaneous growth and division of the 

 nerve-fibre belonging to the parent muscular fibre, in order that each of 

 the young muscular fibres may obtain its branch of nerve" (Croonian 

 Lecture, May 1862). 



So far from the narrow young muscular fibres resulting from the division 

 of old ones, the young muscles and young nerves are developed from col- 

 lections of nuclei or masses of germinal matter, precisely resembling those 

 which are found in the embryo. I believe this to be an invariable law. 

 Many facts make me feel confident that it is quite impossible that new 

 textures can be formed by the subdivision of old ones. Formation and 

 development take place upon precisely the same principle in young and 

 old tissues, in health and disease, in simple and complex organisms. New 

 muscular fibres may be developed from old ones in this way : the " nuclei" 

 may increase in number, the old muscular tissue may undergo disintegra- 



