126 The American Naturalist. [February, 
In the Arachnids and the Xiphosures, we have evidence of 
several elements in the “brain.” Both Patten and myself 
have shown the existence of three pairs of cerebral ganglia in 
Limulus, in front of the ganglia of the first pair of appendages. 
Patten finds (90) the same number in the brain of the Scor- 
pion, as do Locy (’86, pl. XI, fig. 70) and Kishenouyi (90) in 
Agalena. The copies of Morin’s figures given by Korschelt 
and Heider (’92, fig. 383 B) seem also to be in full harmony. 
On the other hand, Schimkewitsch (87, pl. XXI, fig. 3) repre- 
sents two pairs of ganglia in Epeira in front of the ganglia of 
the first pair of appendages, while in the diagrammatic figure 
(pl. XXIII, fig. 5) he apparently indicates four pairs of pre- 
appendicular ganglia. 
In other groups of Arthropods I know of no detailed obser- 
vations which can be used to aid in the enumeration of the 
neuromeres in the anterior region of the body. If we assume 
‘that in the cases of Hexapods, Crustacea, Xiphosures and 
Arachnids, the neuromeres enumerated above represent the 
total somites in this region, we may then compare, somite by 
by somite, these groups in the following manner : 
HEXAPOD. ARACHNID. XIPHOSURE. CRUSTACEA. 
fae 
Neuromere I | No Appendage | No Appendage | No Appendage | No Appendage 
n IT | Antenna No Appendage | No Appendage | No Appendage 
“III | Appendage No Appendage | No Appendage Antennula 
“IV | Mandible Chelicera lst Leg ntenna 
“Vİ Maxilla Pedipalpus 2d Leg Mandible 
VI | Labium Ist Leg 3d Leg Maxilla 1 
w  VIT | Ist Leg 2d Leg 4th Leg Maxilla 2 
“ VIII} 2d Leg 3d Leg 5th Leg Maxilliped 1 
“IX | 3d Leg 4th Leg 6th Leg Maxilliped 2 
waste eee 
Of course it will be understood that this grouping is limited 
by our present knowledge, and that at any time discoveries 
may be made which will overturn it. It is, however, to bè 
noted that it brings the hinder margins of the thorax of the 
Hexapoda and of the cephalothorax of Limulus and of the 
