96 Dr. Griffith on the Formation of 



who considers them formed by spaces left between filaments 

 " not only having a spiral direction with respect to the duct 

 in which they are formed, but bent upon themselves forming 

 sinuous curves," I have not been able to verify. The fibres here 

 spoken of, although I have carefully sought for them, I have 

 never been able to perceive. Moreover, Dr. Willshire does not 

 attempt to account for the dot. Dr. Martin Barry* has also 

 advanced a theory of the formation of what he has termed 

 dotted ducts, but by reference to his figure it will be perceived 

 that he alludes to that variety which has no rim, and which, 

 according to Hugo MohPs definition, is not the real dotted 

 duct. He says, " the spirals in vegetables are produced in 

 the same manner as the muscular fibres (of animals). Were 

 the division of the spiral, or at least the separation, to be com- 

 plete in some parts and not in others, the appearance would 

 resemble that denominated the reticulated duct, and the ten- 

 dency (as it is supposed) of vegetable fibre to anastomosis 

 might be explainedf." By acting upon a spiral vessel with 

 a spirituous solution of corrosive sublimate, Dr. Barry pro- 

 duces what he terms a double spiral, whose coils appear to 

 interlace, and by their close contact to produce the appear- 



» Trans, of Royal Society of London, 1842, Part I. 



f Through the kindness of Dr. M. Barry I have examined his prepara- 

 tions exhibiting the interlacement of double spirals ; but, although the ap- 

 pearance presented in one or two of them is exactly similar to that which 

 would be seen when a fibre formed in the manner described by him, and of 

 the same size as his, was examined under the microscope, nevertheless 

 there are one or two points which strongly militate against the idea of their 

 being really double spirals. In one beautiful preparation made by Professor 

 Sharpey from the tadpole, the upper portion of one of the fibrillar exhibited 

 an apparent interlacement most distinctly, so much so, that I am sure no 

 prejudiced eye even could have viewed this alone without coming to the con- 

 clusion that it was formed in the manner described by Dr. Barry. But upon 

 viewing the fibre lower down, the interlacing appearance was replaced by 

 that of a rope wherein the fibres all took one oblique direction, leaving 

 spaces between them. When this lower part was carefully brought in and 

 out of focus, at first the oblique portions of fibre above described were seen, 

 but afterwards no alteration would bring into focus the posterior portions of 

 the coil, which satisfactorily convinced me that they were really not spiral 

 fibres. When we examine spirals, however minute, from vegetables under 

 the microscope, we can first bring into focus the upper portion of the coils, 

 and then by depressing the object-glass distinctly perceive the lower ; but 

 in the case of the specimen spoken of this could not be done. I cannot help 

 believing that in this lower portion the fibre really has separated into discs, 

 whose edges give the peculiar rope-like appearance; but I cannot explain the 

 cause of the peculiar appearance of the upper portion. The fact of the fibres 

 of muscles splitting into discs, is, I think, a proof that they cannot be spirals. 

 To break up into discs, the fibrillae must be weaker in one portion than an- 

 other, and I have no doubt this weak part is opposite the dark line on the 

 fibrils, where they are thinnest ; but I do not believe the fibrils are beaded, 

 I think they are merely transversely thinned opposite the dark portions, and 

 that the beaded appearance is an optical illusion. 



