OBSERVATIONS ON THE NERVOUS SYSTEM OF APUS. 435 
rior Crustacea is to be regarded as formed by the fusion of 
the ganglia situated before the mandibular ganglion, a fusion 
which is connected with the welding of the cephalic segments. 
In Apus the optic nerves only are seen coming out 
of the brain. There are then good reasons to think 
that this brain is a simply primitive brain. 1 
IV. Since one sees the nerves of the two pairs of antennae 
of Apus coming, not out of the brain, but rather far behind 
it, out of the abdominal cord, the two pairs of antennae 
are metastomial appendages, which, in superior Crus- 
tacea, became prostomial in consequence of further displace- 
ment. 
I shall now examine successively these different questions : 
I. The first antennary nerve does not immediately turn for- 
ward when it comes out of the cord as it is shown in Zaddach’s 
figure (loc. cit., pi. iii, fig. 5, b ). On the contrary, it goes 
from forward backwards, showing a curve of a quarter of a 
circle, and going finally forward. This disposition is easily 
understood when one examines with a small magnification 
that part of the nervous system of Apus. One may then 
observe (fig. 1) that the fibres composing the first antennary 
nerve (a i), after having entered the abdominal cord (c a), 
proceed from behind forwards, and then towards the brain 
(c). They may be followed very far and teazed away from 
the other fibres composing the cord. At the point where the 
nerve joins the cord, one remarks upon the internal side of 
the latter, between the envelope and the nervous fibres, a large 
nerve ganglion-cell (c n) which has no relation with the 
first antennary nerve (a i). 
The ganglionic cells from which this nerve comes off are 
not to be found in the elongated ganglion (r a, fig. 1) but in 
the brain. Therefore, if the latter is an archicerebrum, the 
1 Professor Ray Lankester calls these brains when formed by the single 
pair of primitive cephalic ganglia, archicerebrum, in opposition to the 
syncerebrum, or complex brain formed by the union of several pairs of 
ganglia (“ Observations and Reflections on the Appendages and on the 
Nervous System of Apus cancriformis,” this Journal, 1881). 
