114 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
body. In Rhynchelmis, too, according to Vejdovsky (88, ’92), the giant 
fibres are connected with a number of cells and in such a way that 
each might well be considered a bundle of fibres. Finally, Lewis (96) 
describes in a Moldanid a giant fibre which is connected with a large 
number of cells. There is not yet sufficient evidence to show whether 
the giant fibres of Cheetopods are more frequently multicellular or uni- 
cellular, but there can be no doubt that they are often multicellular. 
The giant fibres of Crustacea have not been so well investigated as 
those of Chzetopoda, but in Homarus, at least, each giant fibre is the 
process of a single large céll, according to the description of Allen (’94). 
Our present knowledge of the giant fibres (in the sense in which I use 
the term) might be summarized in the following way. The giant fibres 
of Annelids and Crustacea are much larger than ordinary fibres, and ex- 
tend for long distances through the central nerve cord ; they are con- 
nected either with one very large cell or with the processes of several 
cells, and they give off neither fibrillations nor branches. In some cases, 
as in Lumbricus, there are anastomosing bars, or connections, between 
two giant fibres; in others, the giant fibres may divide or they may fuse 
with one another, but in no case is there an ending corresponding to the 
fibrillations of other nerve fibres by which the giant fibres might be put 
in connection with other nervous structures. In Nereis, however, there 
is a very intimate connection between the lateral giant fibres and the 
centrifugal branches of set B, as I have shown, and by this system of 
connections the giant fibres are put in relation with every segment of the 
body. 
What the function of such giant fibres may be is readily conceivable, 
and I believe the true explanation has already been offered by several 
writers. Vignal (’83) suggested that their purpose was to bring about 
a more direct connection of the nervous system as a whole than is done 
by less extensive fibres. Friedlander’s experiments on the earthworm 
show that, when the ventral cord is severed, the sudden longitudinal 
contraction of the body can no longer be brought about. Friedlander 
argues that, since these fibres are the only ones, so far as we know, that 
pass through the entire length of the animal, it is reasonable to suppose 
they are the ones that conduct the stimulus for this contraction. 
In Nereis I have frequently noted a sudden longitudinal contraction 
where there was apparently no stimulus except the passing of a shadow. 
I have. not yet had the opportunity to test this further, to determine if 
the stimulus proceeded from the eyes, but I found that no tactile stim- 
ulus was sufficient to produce such a sudden and general longitudinal 
