LIMULUS AN ARACHNID. 511 
with that of Limulus we find portions precisely correspond- 
ing to the three main regions above distinguished in the 
latter animal. Anteriorly we have (a) a cerebral mass 
supplying the central and marginal eyes with nerves, (B) a 
large cesophageal collar, from which radiate the nerves to 
the appendages and some other parts, and (c) an abdominal 
cord which terminates in the fourth of the narrow preanal 
segments of the body. 
When we lock into details a little more closely we find 
some very obvious differences between these regions as pre- 
sented in the Scorpion on the one hand and in Limulus on 
the other. But it must be remembered, in regard to these 
differences, that we have no account of the Scorpion’s nerve- 
centres derived from the dissection of fresh specimens, nor 
of the actual arrangement of nerve-cells and nerve-fibres as 
revealed by microscopic examination. 
In the first place the brain and the esophageal collar of 
Scorpio are more intimately fused with one another than 
are the corresponding parts of Limulus. Moreover, the 
esophageal collar is relatively more massive, and exhibits 
but a small perforation for the passage of the very narrow 
esophagus. Instead of being bridged over behind the ceso- 
phagus by transverse commissures, as in Limulus, the two 
halves of the collar appear to be flattened out here and 
fused with one another. It is possible that a more accurate 
knowledge of this region in Scorpio might show structure 
representing the transverse commissures of Limulus. 
A long tract of the most anterior portion of the abdo- 
minal cord in Scorpio, as in Limulus, gives off no nerves. 
But in accordance with the elongated form and well- 
marked segmentation of the hinder region of the body, we 
find that after this first tract there are, in Scorpio, seven 
well-marked ganglia placed at intervals on the cord, the 
most anterior of them sending off nerves to the third pair of 
lung-sacs, but to nothing in front of this. 
With regard to the actual origin of nerves, it has always 
been stated that the first pair of appendages of Scorpio 
receive each a nerve from the pre-cesophageal ganglion. If 
this were absolutely the case it would mark a considerable 
difference between Scorpio and Limulus. But as a matter 
of fact mere inspection of Newport’s drawing is sufficient to 
show that the nerves to the chelicerze of the Scorpion have 
a lateral position embracing the true “ archi-cerebrum,” 
which supplies the lateral and central eyes between them, 
and whatever may be the result to be obtained in the future 
by microscopic sections or study of fresh specimens, we have 
