STUDIES ON THE NERVOUS SYSTEM OF CRUSTACEA. 493° 
almost spherical, and are connected by moderately long 
threads ; whilst in fig. 9 they have the form of elongated 
spindles, and the threads are shorter. In both cases it will 
be noticed that the beads vary greatly in size and shape, and 
that the length of the connecting threads also varies. 
Fig. 11 represents a nerve-fibre ending in the commissural 
ganglion, in which the beading has been carried to a somewhat 
remarkable extent, out of all proportion to the size of the 
fibre. 
Fig. 10, a, B, c, represents three portions of one fibre, which 
was stained in an cesophageal commissure of Astacus. Near 
the brain the fibre is practically cylindrical (first portion of A). 
The undulations become more strongly marked, producing the 
appearance of elongated spindles lying close together (B) as 
we pass further back; whilst near the commissural ganglion 
the spindles are joined together by fairly long threads, and the 
result is a typical beaded fibre (C). Thus we have the various 
stages all represented on a single fibre. Such cases are not 
uncommon, and they alone make it practically certain that the 
cylindrical form is the normal condition of the fibre, the beaded 
condition being due to some external cause. It was observed 
that when the object was unduly stretched or pulled about in 
the process of preparation, the number of beaded fibres very 
largely increased.1 
My observations on embryonic and larval forms have been 
1 The larger fibres, when stained with methylene blue and preserved in 
ammonium picrate, generally have the surface covered with deeply stained 
granules, which are either arranged irregularly, as in figs. 8—11, or may lie in 
longitudinal rows, as in fig. 7. It is not possible to say, in my opinion, 
whether these are entirely artificial, or whether they may be taken as an 
indication of the structure of the protoplasm composing the fibre. The latter 
view has been held by Dogiel (‘ Arch. mikr. Anat.,’ 41, 1893), who appears to 
consider the fibrillar structure as demonstrated. I should like to draw the 
attention of those interested in this question to the large black chromatophore 
masses of Mysis flexuosa. When these are expanded, the pigmented pro- 
toplasm in the larger processes is arranged in parallel strands. After soaking 
for some time in sea water, these strands break up into short pieces and give 
rise to an appearance which resembles very closely that represented on the 
nerve-fibre in fig. 7. 
