STUDIES ON THE NERVOUS SYSTEM OF CRUSTACEA. 495 
in selecting suitable objects for study, those animals in which 
the nerve-fibres are coarsest will be most likely to give good 
results. 
Ramon! has also noticed, in studying the retina of Verte- 
brates, that the more delicate the structure, the more difficult 
it becomes to obtain satisfactory impregnation by Golgi’s 
method. This tendency on the part of fine nerve-fibres to 
break up into drops appears to me to explain, to a large extent, 
the impossibility of satisfactorily making out any structure in 
the neuropile (punkt-substance) when preserved by ordinary 
methods. 
Another phenomenon, which at first sight closely resembles 
the beading of nerve-fibres, is the formation of small swellings 
on the terminal branches of a nerve-ending. These have been 
often described, and for a number of typical instances I may 
refer to fig. 6, and the finer branches of fig. 11. It will be 
seen that these swellings usually occur at the angles, where 
fine twigs are given off, and it is not unlikely that this is 
always the case, though in some instances the branch has not 
stained. 
From the facts recorded above concerning the beading of 
fibres, especially the direct observation that the finer branches 
do assume the varicose appearance much more rapidly than 
any others, I should have been led to cousider it probable that 
these end-swellings were post-mortem products, and were 
found in that particular position so constantly on account of 
the fineness of the fibres. In examining living lobster em- 
bryos, however, I was struck with the appearance presented by 
the terminal branches of the bright red pigment cells or chro- 
matophores, which occur in large numbers. Fig. 12 (a) repre- 
sents such a chromatophore, whilst fig. 12 (b), (c), (d), (e), and 
(f) shows individual terminal branches of other cells. Such 
appearances can be observed in favorable cases even before 
the embryo is removed from the egg membranes, and when 
there cannot be the slightest doubt that the animal is alive 
1 Ramon y Cajal, ‘ La Cellule,’ ix, 1893 (quoted in ‘ Journ. Micr, Soc.,’ 
pt.5, 1893). 
