OBSERVATIONS ON THE NERVOUS SYSTEM OF APUS. 439 
ceeds as far as the posterior end of the brain (figs. 4 and 
5, g 2). 
We have there a true second pair of ganglia held in the 
brain. The cells which form it are not small cells of the super- 
ficial layer ; they are large pyriform cells attaining some 
thickness. These two ganglionic masses do not belong to the 
primitive cephalic ganglia, like the mass at the beginning of the 
optic nerves ; they are, on the contrary, far from them, and 
entirely separated (see fig. 6, g 1, and g 2). They are then 
wholly independent of the primitive cephalic ganglia. 
What is that second pair of ganglia ? 
If one examines a longitudinal section near the ventral 
surface of the brain (fig. 8) one can see that the prolongations 
of the cells composing these ganglia proceed backward, and 
that the nervous fibres which come from them go into the cord 
on the side whence come the fibres of the first antennary 
nerve. We have, therefore, here the ganglion of this 
appendage. 
Therefore the brain of Apus is a complex brain, a syncere- 
brum formed by the juxtaposition of two pairs of ganglia, the 
formative elements of which remain separate. These two 
pairs of ganglia are the primitive cephalic ganglia and the 
ganglia of the first antennary pair, or first pair of the 
abdomin al cord. 
This proves obviously that the second pair of ganglionic 
masses in the brain is a pair of the abdominal cord, which has 
moved into juxtaposition with the primitive cephalic ganglia. 
These two groups (g 2, fig. 5) are not joined, as is the case 
for the last (g 1) ; they are very far from one another, and 
situated on the external edges of the brain, showing the same 
disposition as the ganglia of the abdominal cord. A horizontal 
section passing through one of the thoracic ganglia (fig. 9) shows 
the ganglionic cells situated on the lateral edges, just as is 
the case with the second pair of ganglionic masses of the brain. 
As for the group of small cells situated on the posterior edge 
of the brain (fig. 7, a p), I do not give to it a special morpho- 
logical signification. It is only a part of the superficial invest- 
VOL. XXV. 
NEW SER. 
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