TRANSACTIONS OF SECTION I. 951 
The reason for this grouping is seen when we turn to Limulus and its allies, for 
we find that the body is always divided into a prosoma and mesosoma, and that 
the appendage nerves are divisible into two corresponding well-marked groups, 
viz. -— 
1. A posterior or mesosomatic group, which arise from the mesosomatic ganglia 
and supply the operculum and branchial appendages. 
Fi@. 3.—Head Region of Ammoceetes, split longitudinally into a ventral 
and dorsal half. (Ventral Half.) 
= = 
=| = 
= =| 
= = 
yy 3 SE =\ 
Appendages § Nerves (2 =) 
TENTACULAR |= = 
v™ 1-4 ff 
VELAR Jie 
yu 5 i 
OPERCULAR fff CILIATED 
Vile GROOVE 
BRANCHIAL 
Ist BRANCAHIAL — = | OPENINGS 
Ix 
2nd BRANCHIAL 
xt -2 
3rd BRANCHIAL fe he a es a —— 3 
! All=ank: 3 
= THYROID 
ORIFICE 
4th BRANCHIAL 
x3 
5th BRANCHIA 
xi 
6th BRANCHIAL 
x5 
7th BRANCHIAL 
xe 
2. An anterior or prosomatic group, which arise from the prosomatic ganglia 
and supply the oral or locomotor appendages. 
