HAMAKER: NERVOUS SYSTEM OF NEREIS VIRENS. 111 
Racowitza shows that those Polychætes which lack antennæ also lack 
the “ ganglion antennaire.” He does not prove, however, that the cells 
of this ganglion may not be present in the brain, and therefore does not 
exclude the possibility that the ganglion may be present in a diffuse 
form. 
5. Optic GANGLION. 
The condition of the optic ganglion in Noreis virens is of interest, 
because it serves to explain what have hitherto appeared to be unac- 
countable differences between several species of Nereis. Carrière (’85, 
pp: 33-35) described this ganglion for N. cultrifera, and Retzius (95) 
found it in N. diversicolor. On the other hand, Carriére says there is 
no such ganglion in a species from Norderney which he examined, and 
Graber (’80) and Haller (’89) also failed to find it in Nereis coste. It 
seemed strange that a central ganglion, like this, should exhibit such 
will-of-the-wisp peculiarities in passing from one species to another so 
closely related to it. I think, however, that the condition of this gan- 
glion in N. virens shows clearly what becomes of the ganglion when it 
disappears from its place beneath the anterior eye, as in N. coste. In 
N. virens the ganglion evidently lies partly beneath the eye and partly 
within the brain capsule. A few scattering cells show the path the gan- 
glion has taken in its migration inward or outward. It is not only the 
great similarity in the appearance of the cells and the contiguity of the 
two parts that makes this view seem probable, but also the cells of both 
groups send their processes to the commissural ganglion and neither part 
appears to be directly connected with the brain. It is not apparent what 
is the relation of the ganglion to the anterior eye. Carrière thought 
the ganglion formed part of the connection between the eye and the 
brain, but this cannot be, for later writers agree that the anterior eye 
as well as the posterior is innervated directly from the brain. 
The posterior end of the brain deserves more careful study than I 
have as yet been able to give it; I shall therefore simply call attention 
to a few facts. Five of the six kinds of cells described for the brain are 
to be found in the posterior part, and of these five three are not found 
elsewhere. Moreover these three are the most peculiar ones, — those of 
the second, third, and fourth classes. This portion of the brain is partly 
separated from the remainder of it, and is intimately connected with 
the surface at the ciliated grooves and at the dorsal sensory regions 
through the thirteenth (XIII) and fourteenth (XIV) nerves. Perhaps 
