512 PROFESSOR E. RAY LANKESTER, 
the important embryological fact due to Metschnikoff (and 
confirmed for other Arachnida by Balfour) that the nerve- 
ganglion mass from which the nerve to the chelicera on each 
side takes its origin is guite independent of the archi-cere- 
brum, and in the embryo is placed behind the latter, and to 
the side of the cesophagus right and left. This seems to me 
sufficient to justify a complete assimilation of the two regions 
in Scorpio and Limulus, the difference being merely that post- 
embryonic fusion of the archi-cerebrum and lateral ganglia 
has proceeded a little further in Scorpio than in Limulus. 
From the collar, then,in Scorpio, as in Limulus, the 
nerves to all six of the pediform appendages take their 
origin. But the agreement extends even further than this, 
for the nerves to that region of the Scorpion’s body which 
corresponds with the genital operculum of Limulus also 
proceed from the cesophageal collar. The attraction (if 1 
may use the term) of nerve origins to the cesophageal collar 
appears to have proceeded further in the Scorpion than in 
Limulus, for, whereas, in Limulus, the first and remaining 
four pairs of branchial feet are supplied from the abdominal 
cord, in Scorpio those parts, which for reasons to be given 
below, I consider to represent the first, second, and third of 
the branchial feet of Limulus, all appear to receive their 
nerves from the esophageal collar, so that it is not until 
we come to the representatives of the fourth pair of bran- 
chial feet of Limulus (viz. the third pair of lung-books, see 
below) that we find in the Scorpion a nerve supply from 
the abdominal cord. This phenomenon of the travelling 
forward and concentration of nerve origins and their con- 
nected ganglia is one sufficiently familiar in various groups 
of animals. The fact of the dislocation in this way of the 
nerve supply of the genital operculum of Limulus above 
remarked on, receives illustration by the still further carry- 
ing out of the same process in Scorpio. 
The difference in the disposition of the nerve orgins (such 
as it is) in regard to the hinder part of the abdominal cord 
in the two animals receives its explanation from the differ- 
ence of general form and segmentation of the hinder region 
of the body which they respectively exhibit. 
It appears, then, that there is when the most recent results 
of anatomical and of embryological observation are taken 
into consideration, no important difference between the 
central nervous system of Limulus and of Scorpio, and more 
especially it is to be noted for the purpose which we have 
next in view, viz. that of comparing the skeleton and ap- 
pendages of the two animals, that there is not a difference of 
