OF WASHINGTON. 109 
cupy their natural position, are here pushed into other places, or overlap, 
or are abbreviated, atrophied, or altered to such a degree that their true 
character can only, with difficulty, be rightly determined. And, if we now 
examine the posterior region, it contains internally no organ which could 
not be, and is not in the closely allied forms, abbreviated to half its length ; 
it bears externally no other important part, except the sole defensor, the 
poisonous sting, and probably the body was so elongated that this weapon 
might be able to protect the animal from an attack upon any part of its 
body. 
The whole body of the Scorpion is covered by a tough, coriaceous mem- 
brane, which is prone to develop into plate-like structures, sclerites, of a 
hard chitinous consistence. These sclerites cover the dorsal and ventral 
parts of the body and the appendages and only the pleural sides of the 
cephalothorax and the abdomen, and the articulations of the latter are free 
and enveloped by the athrodial membrane. These sclerites form the ex- 
ternal skeleton of the Scorpion. 
Viewing the body from a general morphological standpoint, we find it 
naturally divided into three distinct regions : the cephalothorax or pro- 
soma, the abdomen or mesosoma, and the tail o<~ metasoma. Each of 
these regions consisted originally of six segments, but the condition of 
concentration in the prosoma has obliterated these articulations, and they 
are only indicated by the six pairs of appendages which it bears. The 
meso- and metasoma consist of apparently thirteen segments, but the 
terminal joint of the tail, the vesica, with the long and sharp sting, can- 
not be counted with the abdominal segments on account of its post-anal 
position; it is an abdominal appendage. 
The cephalothorax is covered dorsally by a solitary chitinous plate, the 
Carapace, into which the organs of vision are inserted. They consist 
of three groups of simple eyes, corresponding with the ocelli of the 
insects. A large pair is situated in the median line of the carapax, either 
at, or before, or behind the centre of the longitudinal axis; on each side, 
at the latero-anterior-angle of the carapace is a group of two or three ocelli, 
with sometimes one or two accessory ones, like those of Thelyphonns which 
I mentioned on a former occasion. I have here to withdraw a statement 
made at a previous meeting, that these accessory eyes are not provided 
with a separate branch of the optic nerve, and are, consequently, mere 
granular integumentary formations an opinion which other naturalists 
also entertain but in Androctonus, which generally possesses two acces- 
sory ocelli, I have found a distinct branch to both. This fact, however, 
has been long known, and in 1843 Newport, of England, described, in his 
excellent paper, the lateral ocular branches of the optic nerve. 
The six pairs of appendages of the prosoma are : the mandibles, the 
maxillae, and the four pairs of legs. The mandibles are three-jointed, 
and the two joints form a chela or forceps. Let me here mention that a 
very important point in the present classification is based on the tooth 
armature of both of the mandibular fingers; indeed, the existence of sub- 
