102 DR. MARTIN BARRY ON FIBRE. 



usually breaks off short. The membranous partitions or septa, above described (par. 

 42), no doubt contribute to prevent a difference in length. Besides which, fig. 123. 

 shows that there are states in which the flat filaments (" fibrillae") are shared by more 

 than one surrounding spiral. See the additional observations, par. 119. I would also 

 suggest that the spiral form of the ultimate threads of muscle, shows why it is that, 

 before being broken off, the fasciculus sometimes becomes tapered to a point. An in- 

 stance of this kind is to be seen in fig. 67, representing two portions of the same fas- 

 ciculus. In a, the direction of the curves of the spirals is comparatively transverse ; 

 and this part of the fasciculus is thick : in (3, the direction of the curves becomes more 

 and more oblique, until the fasciculus, rendered in the same proportion thin, termi- 

 nates at last in a point. A very distensible membrane invests the fasciculus to the 

 extremity ; being one of the means by which its spiral contents are held together, 

 during this violent elongation. 



55. In a former paper-f-, I stated that membranes appeared to arise from the coa- 

 lescence of discs. Fully confirming this observation, I have now to add, that, in some 

 instances at least, the discs first form flat filaments, such as those above described ; 

 which filaments become interlaced with other filaments, divide, subdivide, and coa- 

 lesce to form the membranes. The cellular tissue entering into the formation of the 

 sheath of the spinal chord, we saw to become interlaced for this purpose % : and in an 

 earlier series of investigations, I found the incipient chorion to present an appearance 

 somewhat the same. The present memoir contains examples of membrane being 

 formed out of interlacing filaments. Muscle presents an instance of membrane, that 

 of the fasciculus, forming by the interlacement of mere spiral threads, many of which 

 are too minute to admit of their structure being investigated. But the larger of these 

 threads present a compound structure (figs. 125, 68), which admits of being traced 

 into the objects I have termed flat filaments : and minuteness is no hindrance to the 

 smallest undergoing a like change. The origin of this membrane out of spirals, 

 may assist to account for its remarkable distensibility, elasticity, and toughness, 

 pointed out by BOWMAN. This author indeed remarks, concerning it, that though 

 from its minuteness and transparency, " it is difficult to form any decided opinion as 

 to its structure *** it would seem not improbably to consist of a very close and intri- 

 cate interweaving of threads far too minute for separate recognition." But he adds, 

 that " the matter is very doubtful ||." 



56. In the mammiferous ovum, we saw the first cells succeeding the germinal vesi- 

 cle to be few and large ; and that there occurred a doubling of their number with 

 every diminution in their size^j". The same process, essentially, we have since found 



t Philosophical Transactions, 1841, pp. 209, 230, 243. J Ibid., 1841, Plate XXII. fig. 116. 



Ibid., 1840, Plate XXVIII. fig. 252. || L. c., p. 478. 



f Philosophical Transactions, 1840, p. 539. 



