OF WASHINGTON. Ill 
inside of the mouth, we may easily see the true structure (Fig. 3, e, the 
labium). 
In no other order of Arachnids is the fact 
so nicely, so distinctly demonstrated, ad 
oculos, that the first pair of legs will soon 
(in a higher class) develop into labial palpi, 
as in the Scorpions ; for here we see clearly 
the insertion of these appendages into the 
sides of the labium (Figs, i and 2). F '%?u^eeT? r 7m 
That the part which occupies the median the mouth; I, coxae of the first 
pair of legs, 
area of the labium is the prosternum, is proven 
by the insertion of the second coxae, that is, the coxae of the first true 
legs, which insertion is clearly illustrated in some genera of the family 
Pandinoidce, in which the labial border surrounds the basal part of the 
coxae (Fig. 2, sternal side of Hormurus Underivoodit n. sp.) The meso- 
sternum is not always visible, at least not at the external surface: and 
where it is distinctly present it has been hitherto overlooked by observ- 
ers. In the 'family Androctonoidce we distinctly see in many genera a 
small tubercular process right at the anterior border of the " sternum " 
the metasternum (Fig. i, b}. In the family Pandinoida, where the 
metasternum is less reduced in size than in the former, the mesosternum 
is blended with the metasternum, and is indicated visibly in many gen- 
era by a distinct line and a difference in the angular position of these two 
areas (Fig. 2, , mesosternum). 
The metasternum is the great criterion for the families into which the 
order of the Scorpions is divided. Is it long and very narrow, or sub-tri- 
angular, the animal belongs to the family Androctonoidce ; if it is pentag- 
onal, the family Pandinoidcz is indicated; while those scorpions without a 
metasternum, or in which it is only represented by two transverse linear 
structures, are included in the third family, Bothriuroidce. 
The second general region of the body, the mesosoma or abdomen, with 
its seven segments at the dorsal surface (some naturalists consider the last 
segment as belonging to the tail), has ventrally apparently only five scler- 
ites. But we notice in the narrow space between the last pair of coxae and 
immediately behind the metasternum two peculiar structures, the anterior 
of which represents the genital operculum (Fig. i, */), and below which 
lies the sexual apparatus. As this operculum is of the same form in both 
sexes, the scorpion cannot be sexually differentiated by this organ. Be- 
hind the operculum, which is generally of an oval, plate-like form, are sit- 
uated those peculiar organs which are original to the Scorpion, the combs 
(Fig. i , /). Of the functions of these organs we know absolutely nothing. 
By the concentration of the cephalothorax the space for the two an- 
terior ventral sclerites becomes so scarce and narrow that only the genital 
tubercle of the first ventral segment and the jugum with the combs of the 
second segment are retained, while the rest of the space is occupied by the 
third and fourth coxae. 
