110 DE. WILSON FOX ON THE DEVELOPMENT 



which I have been led to entertain agree with or differ from theirs ; but I think it may 

 be desirable for me to refer to two papers which have already appeared at the meetings 

 of this Society, and in which the views expressed by their authors are somewhat at 

 variance with those which my observations have led me to form. 



Mr. Savory's* observations were made on the dorsal muscles of embryos at a period 

 when their development is already considerably advanced. It will be seen that my 

 figures of the Chick and Sheep in more advanced stages correspond very closely to his 

 drawings, though I have not thought it necessary to multiply figures of the enlarge- 

 ment and maturation of the fibres, as these have been already most ably depicted in the 

 paper in question. 



There is one other observer, whose distinguished position entitles his observations to 

 the greatest respect, but with whose views my own cannot be brought to correspond. I 

 refer to Mr. Lockhart Clarke, who, in vol. xi. of the ' Proceedings ' of this Society f, has 

 advanced the view that the development of the fibre proceeds by a fibrillation of blastema 

 upon free nuclei. There is at once a discrepancy between Mr. Clarke's observations and 

 mine as to the period at which a distinct difiierentiation of muscular tissue occurs, he 

 placing it at the fifth day of incubation, while I have found it distinctly advanced after 

 forty-eight hours. Mr. Clarke regards such figures as 24 & 25 in my Plates as the 

 result of the deposition of granular matter around a nucleus, the granular matter form- 

 ing a fibre and embracing the nucleus ; I regard them as the further elongation of such 

 cells as figs. 22 & 23 represent. I have already given my reasons for regarding these 

 structures as possessed of a sharp limiting outline, though, of course, in breaking up 

 such delicate structures for microscopic examination, free nuclei surrounded by more or 

 less granular matter will frequently be more numerous objects in the field than the com- 

 plete cell-forms, which are often comparatively rare and difficult to find, but which I 

 regard, as will be seen from the foregoing, as the essential element in the development 

 of these structures. 



Description of the Plates. 



PLATE V. 



" Figs. 1-21 represent the development of muscular fibre in the Tadpole, 



X 900 diameters. 

 Fig. 1. First appearance of muscular tissue at extremity of tail of newly-born Tadpole. 

 Outline well defined, though membrane not apparent. Measures j:^ of an 

 inch in length, g^ of an inch in breadth. Nucleus measures 3^ X Woo 

 of an inch. 

 * Philosophical Transactions, 1855. t Also in Microscop. Joum. 1862. 



