374 Dr. Fox on the Development of [June 15, 



manner with the Scolecida since, although in the points above mentioned 

 they display their affinities to the Echinoderms, still, as regards the struc- 

 ture and different modifications of the ventral excretory apparatus, they 

 agree more closely with the Trematoda or flukes. 



XV. " On the Development of Striated Muscular Fibre." By WILSON 

 Fox, M.D., Professor of Pathological Anatomy in University 

 College, London. Communicated by Dr. SHARPEY. Received 

 June 15, 1865. 



(Abstract.) 



The discrepancies in the statements made by various observers on the 

 structure, as illustrated by the history of the development, of striated mus- 

 cular fibre, have induced the author to submit the question to a renewed 

 and independent investigation. He has examined the process in the tad- 

 pole, the chick, the sheep, and in man, and with results which correspond 

 very closely in all these classes. The investigation is most easy in the tad- 

 pole, as the early structures are of much larger size ; but observations are 

 made with a comparatively greater precision when high magnifying powers 

 are employed. The author has used 900 linear in his observations on 

 the tadpole, 1250 or 1850 linear in his observations on the chick and 

 mammalia. The earliest form in which muscular tissue appears in the 

 tadpole is an oval body containing one or more nuclei, and densely filled 

 with pigmentary matter. This body has a well-defined outline, which in- 

 duces the author to regard it as a cell, though he has not succeeded iu 

 isolating any distinct membrane. Such bodies then increase in length 

 with or without multiplication of their nuclei, and after a short period a 

 portion of their structure loses in great part its pigment and exhibits a 

 striation sometimes transverse, sometimes longitudinal, or occasionally both 

 conjointly ; but there is no distinct line of demarcation at this stage between 

 the striated and non- striated portion of the cell-contents, showing that the 

 change takes place within the contents of the cell. 



As the pigment gradually diminishes in the non-striated portion of the 

 cell-contents, a membrane can in some cases be very distinctly observed 

 limiting the whole structure, while in others it can only be seen around 

 the non-striated portion, and in the former case the presence of a striated 

 structure within this membrane is very distinct. The nuclei are always found 

 situated in the granular non-striated portion of the contents of the cell. 



The cell may elongate to a very long fibre, to which only a single nucleus 

 may be attached, or in the process of elongation a great increase in the 

 number of nuclei may take place. In all cases the nucleus and fibre are 

 enclosed by a membrane, which the author regards as an extension of the 

 original membrane enclosing the cell in its earlier stages. The thickness of 

 the striated portion appears to be in direct proportion to the number of 

 nuclei enclosed within the membrane. 



With the advance of development the space occupied within the mem- 



