HAMAKER: NERVOUS SYSTEM OF NEREIS VIRENS. 119 
3. The “mushroom bodies” of insects and decapod Crustacea are 
represented in the brain of Nereis by the anterior masses of small 
nuclei. 
4. The optic ganglion, which in some species of Nereis lies beneath 
the anterior eye, may in other species lie within the brain capsule. 
5. There is no neuropil in the ventral nerve cord. 
6. There are three longitudinal connectives between each two succes- 
sive ganglia of the ventral nerve cord, one small median and two larger 
lateral ones. 
7. The sheaths of the nerve fibres of the ventral cord have no nuclei, 
and hence must be a product of the fibres themselves. 
8. The nerve cells of the ventral cord commonly have one or more 
centrosomes. 
9, The giant fibres are nervous in function, and are put into relation 
with peripheral organs through ordinary centrifugal fibres. 
10. The giant fibres give off no fibrillations, and nervous relation with 
other fibres is established directly between the axis cylinders. 
11. Certain decussating fibres are always united in pairs by anasto- 
moses between the axis cylinders where they cross each other. 
12. Certain centripetal fibres of the same set are always united by 
anastomoses between the ends of the branches. 
13. Contact between axis cylinders may possibly be one of the means 
of bringing nerve fibres into functional relation with each other. 
In conclusion, I wish to acknowledge my indebtedness to Professor 
E. L. Mark for kindly advice and assistance rendered me in many ways 
while pursuing my studies in the Zöological Laboratory of Harvard Uni- 
versity. I gladly avail myself of this opportunity to express to him my 
sincere thanks. 
o 
VOL. XXXII. — NO. 6, 3 
