HAMAKER: NERVOUS SYSTEM OF NEREIS VIRENS. 113 
first, the general occurrence of the centrosome in the cells of the ventral 
ganglia, and, secondly, the large number of centrosomes that may occur 
in a single cell. I have no explanation to offer for the latter condition. 
Since the structures appear only under special conditions of staining, 
and since I had only one preparation of the brain stained in iron-hzma- 
toxylin, I am not in a position to say whether the centrosome occurs in 
the brain or not, even though I failed to find it in the preparations 
I had at hand. 
8. Nerve FIpres. 
a. Giant Fibres. 
The literature concerning giant fibres is voluminous, and extensive 
bibliographies on the subject may be found in the works of Eisig (’87) 
and Friedlander (’88, 94). I shall concern myself here with only a few 
of the many points in which these fibres have given rise to discussion. 
It has been frequently demonstrated that they are the processes of cells, 
and they have been taken by many writers to be nervous in function, 
but some authors still doubt that that is their nature ; Lenhossék (’92), 
for example, has recently expressed the conviction that they are not. 
The most serious objection that has been urged against their nervous 
nature is the absence of evidence that they are related to other ner- 
vous structures, either by fibrillations within the cord or by centrifugal 
branches. 
I think there is sufficient reason for maintaining that in Nereis virens 
the fibres of set B& serve as branches for the lateral giant fibres. I 
therefore believe that the function of the latter is to transmit nervous 
impulses like ordinary nerve fibres. 
The most peculiar feature of giant fibres is that they are often con- 
nected with more than one cell. In 1881, Spengel (’81) arrived at the 
conclusion that in Halla there was a fusion of giant fibres, but he bad 
no direct evidence. Rohde (’87), however, shows conclusively that at 
least one giant fibre in the ventral cord of Sthenelais is formed by the 
union of the processes of two cells. These lie in the brain and send 
their processes through the circum-csophageal connectives to the sub- 
cesophageal ganglion, where they fuse and whence they continue as a 
single fibre throughout the entire length of the animal. Friedliinder 
(88) found that the lateral giant fibres of the earthworm are connected 
with a number of cells in the posterior segments of the animal. This 
discovery was confirmed by Cerfontaine (’92), who also found that the 
median fibre is connected with several cells at the anterior end of the 
