116 DR. MARTIN BARRY ON FIBRE. 



duct. And the observation now recorded, that these structures consist of the remark- 

 able filaments in question, seems sufficient of itself to warrant the belief that they 

 have no such mode of origin. 



116. I have already mentioned having seen these filaments in the shell-membrane 

 of the Bird's egg. This membrane I believe is usually regarded as the analogue of 

 the chorion in Mammalia. Now the chorion of the Mammal, according to my ob- 

 servations, has its origin in corpuscles of the blood : and it is not likely that its ana- 

 logue in the Bird is produced in a different way. 



117. On a former occasion-^-, we saw the incipient chorion, when rising from the 

 " zona pellucida" in the mammiferous ovum, to leave a stratum of unappropriated 

 cells behind it on the " zona," a gelatinous fluid intervening. These cells are sub- 

 sequently appropriated in the thickening of the chorion. I think it possible that it 

 maybe the outer layer of the chorion just mentioned, that is represented by the shell- 

 membrane ; while the stratum of cells left for a while on the " zona" in the mammi- 

 ferous ovum, finds its analogue in the chalazse of the Bird's egg. If so, it will doubt- 

 less be found that the chalazse also have their origin in corpuscles of the blood ; which 

 indeed their structure renders probable. 



118. As already mentioned (par. 53^). many of the figures which accompany the 

 foregoing memoir represent states of voluntary muscle, in which the longitudinal 

 " fibrillae" have no concern in producing the transverse striae. In these states, the 

 transverse striae are caused by comparatively large interlacing spirals, which dip 

 inwards in a manner that may be represented by making the half-bent fingers of the 

 two hands to alternate with one another, and then viewing them on the extensor side. 

 The longitudinal " fibrilke" are contained within the spaces circumscribed by the 

 interlacing spirals. 



119. It is in such states of voluntary muscle, that the fasciculus "breaks off 

 short (fig. 157)-" This breaking off short is a natural consequence of the interlacing 

 of the spirals ; as may be easily shown by a wire model, representing this state of the 

 fasciculus. The fracture of course takes the direction in which there is the least 

 resistance. This direction is the transverse, for in any other there would be a greater 

 number of the curves of spirals to be encountered^:. Sometimes the fasciculus, 

 instead of being "broken off short," is merely notched (fig. 157). These two effects 

 of manipulation, however, differ only in degree ; the cause producing both being the 

 sarne^. This seems to be the explanation of transverse " cleavage." 



t Supplementary Note to a Paper entitled " Researches in Embryology. Third Series : a Contribution to 

 the Physiology of Cells." Philosophical Transactions, 1841, Part II. p. 193. 



J When the longitudinal striae are exceedingly distinct, the fasciculus does not " break off short." This 

 appears to be owing to the absence now of the investing spirals ; which, when present as such, regulate the 

 direction of the fracture. I have already stated them to pass into a membranous form. 



Occasionally the extremities of the ruptured spirals (figs. 156, 157) maybe seen pendent at the part where 

 the fasciculus is broken off or notched. 



