264 Dr.Beale Croonian Lecture. [May 11, 



than free ends, but that the action of the new muscular fibres may be har- 

 monized with those of the other and older elementary muscular fibres 

 of the muscle by branches of nerve-fibres which are probably com- 

 missural. 



I will next venture to consider the nature and origin of the nuclei taking 

 part in the development of the muscular nerves ; and I would remark that 

 in the frog it is comparatively easy to study the formation of even complex 

 organs out of what used to be called a granular blastema. In each suc- 

 ceeding spring-time not only new ganglion-cells but new ganglia and nerve- 

 fibres, as well as vessels, are developed, and take the place of those which 

 attained their perfect condition in the previous year, but which, having 

 performed their work, have wasted and become converted into mere debris, 

 a great part of which was removed during the period of hybernation. 



Now the formation of a new ganglion, of new muscular fibres, of new ves- 

 sels, and other tissues, and even the formation of elementary organs of com- 

 plex structure (as I have ascertained specially in the case of the uriniferous 

 tubes of the newt), results from changes taking place in a collection of 

 small spherical masses of germinal matter ; and these collections themselves 

 seem to result from the division and subdivision of at most a few masses, 

 all of them of course being the descendants of the original germinal mass 

 formed when impregnation occurred. 



Now it may be affirmed most positively, that an entire organ, such as the 

 kidney-tube, or an elementary fibre of muscle, is not formed first and the 

 nerve then spread over it, but the development of the tissue to be influ- 

 enced proceeds puri passu with the development of the nerves which are 

 to influence it. And in the adult animal, where the development of new 

 nerve-fibres takes place, new muscles, &c., are developed in relation with 

 them. I have reason to think, indeed I feel confident, that new nerve- 

 fibres cannot be developed so as to influence an old muscular fibre, or old 

 nerve-fibres caused to influence newly developed muscular tissue ; and in 

 the wasting of certain muscles, or other complex tissues, to which nerves 

 are distributed, as may be studied in the frog, all the old tissue seems to 

 be destroyed and removed by the increase of the germinal matter of the 

 respective tissues. Hence it may be stated positively that in every case 

 the new tissue is developed from a mass of " formless blastema " that is, 

 from a collection of spherical masses of germinal matter which could not 

 be distinguished from the embryonic mass or collection which forms the 

 early condition of every living thing in nature ; and in the destruction 

 and removal of every tissue and organ, masses of germinal matter, often 

 resulting from the division of those of the tissue itself, absorb, remove, 

 and in fact live at the expense of, the tissue which is to disappear ; and 

 whether this change occurs physiologically (that is, as a normal change 

 at certain periods in a healthy and well-developed animal) or pathologi- 

 cally (that is, in an organism which has been subjected to the influence 

 of conditions more or less adverse to its well-being), the process is essen- 



