Royal Microscopical Society. 47 



or by another pigment cell, an appearance leading to the conclusion 

 that the nerve fibre became continuous with the cell, and terminated 

 in it, would be produced. Excessively delicate points of this kind can- 

 not be determined unless specimens of extreme tenuity are examined, 

 and mounted in fluid in which their position can be changed. It is 

 physically impossible to spread such very thin preparations perfectly 

 flat in any limpid fluid, and they can only be manipulated with success 

 in a viscid medium like strong syrup or glycerine. In good speci- 

 mens in these media we may, however, often follow nerve fibres less 

 than the tooVsit of an inch in diameter for a long distance. The edges 

 of the delicate nerve fibre often appear sharp and weU defined, and 

 at certain intervals the nuclei of the fine fibres forming what I 

 believe to be the terminal or ultimate nerve net-w orks, or plexuses, are 

 seen. These bioplasts or nuclei are usually situated more or less 

 on one side, so that the greater part of the nerve fibre is placed 

 upon one side of the nucleus. With regard to the nerve fibrils 

 themselves, many (I believe, all) are unquestionably compound, 

 consisting of still finer fibrils, which are arranged according to the 

 same plan as the nerve fibres in the larger trunks. The consti- 

 tution of these very fine nerve fibres can often be well made out 

 in my specimens (but not in gold or osmium preparations) at the 

 point where one divides into two or more bracches (see PI. VI.). 

 There are few questions more worthy of being thoroughly prose- 

 cuted than this, for by studying carefully the course pursued by 

 the fibres in nerve trunks of various sizes, we cannot fail to 

 ascertain facts of the highest importance, which will greatly in- 

 fluence the conclusions deduced concerning the ultimate distribution 

 and arrangement of nerves. This will in time necessarily lead us 

 to more trustworthy reasoning concerning the nature of nerve 

 action, and the precise way in which some other tissues are in- 

 fluenced, governed, or regulated by the instrumentality of nerve 

 tissue, than will be gained by assuming fads concerning nerve 

 structure, and then determining what according to the idea 

 advanced must be the nature of nerve action, as some who have 

 been considered philosophical have ventured to do. 



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