400 PHILOSOPHICAL TRANSACTIONS. [aNNO 1794, 



as they have membranous tendons, which Mr. Yoimg informs us he distinctly 

 observed, that these tendons cannot possess the same degree of transparency 

 and density with the bellies of these muscles; that is, they must possess some 

 degree of opacity, or certainly he could not have pointed out their membranous 

 structure, nor even the tendon itself, as distinct from the body of the muscle; 

 and if they have not the same density, from their situation, and being of a pen- 

 niform shape, must there not be some irregularity from the difference in the 

 refraction of those rays which pass through the bellies of those muscles, and 

 those again which pass through their membranous tendons? This structure then, 

 of consequence, cannot be well adapted for a body whose regular shape and 

 transparency are of so much consequence. 



Again, Mr. Young describes 6 muscles in each layer; but Leeuwenhoek, 

 whose authority he admits as accurate, relative to the muscularity of the lens, 

 is certainly more to be attended to in his observation of bodies less minute, viz. 

 as to the layers themselves, in which these muscles are found, and which of 

 course are larger, and more easily observed; but, with his accuracy of obser- 

 vation, he has computed that there are near 2000 laminas; and according to 

 Mr. Young, supposing each layer to contain 6 muscles, we have necessarily in 

 all 12,000 muscles; the action of which certainly exceeds human comprehension. 

 I hope this will not be deemed trifling minuteness, as it is a necessary and re- 

 gular consequence, if we admit their existence as described. 



But 2dly, as to the existence of the muscles, I cannot avoid expressing a doubt. 

 With the utmost accuracy I was capable of, and with the assistance of the best 

 glasses, to my disappointment, I cannot bear witness to the same circumstances 

 related by Mr. Young, but found the lens perfectly transparent; at the same 

 time, lest it might be attributed to the want of habit in looking through glasses, 

 I beg leave to observe, that I have been accustomed to the use of them in the 

 examination of the more minute objects of natural history. After failing with 

 the glasses in the natural viscid state of the lens, I had recourse to another ex- 

 pedient; I exposed different lenses before the fire to a moderate degree of heat, 

 by which they became opaque and dry ; in this state it is easy to separate the 

 layers described by Mr. Young; but though not so numerous as noticed by the 

 accurate Leeuwenhoek, still they were too numerous to suppose each to have 

 contained 6 muscles; for I could have shown distinctly at least 50 layers, with- 

 out the assistance of a glass, as was readily granted by those to whom I exhibit- 

 ed them. 



But a circumstance which would seem to prove that these layers possess no 

 distinct muscles, is, that in this opaque state they are not visible, but consist 

 rather of an almost infinite number of concentric fibres (if the term be at all 

 appropriate) not divided into particular bundles, but similar to as many of the 



