ANATOMY AND GENERIC CHARACTERS OF SCORPIONS. 379 
sinuses from drawing upon the blood which has already entered the lateral pericardio- 
pulmonary veins. 
It is not at all improbable that the movements of the body-wall (terga and sterna) in 
Scorpio and of the plastron (prosomatic entochrondrite) in Limulus, and, perhaps, also 
in Scorpio, exert a considerable influence upon the flow of the blood. 
b. Generic and Subgeneric Characters of Scorpions. 
The numerous species of Scorpions which occur in all parts of the world, excepting 
the Arctic and Antarctic regions, and as far back in time as the Upper Silurian strata, 
present a most marvellous uniformity of structure, so that the attempt to divide them 
into families, genera, and subgenera has been a matter of great difficulty, and has led to 
very perplexing and contradictory results in the hands of successive systematists. The 
late Professor Peters appears to me to have indicated the most important divisions 
which may be instituted among Scorpions on structural grounds. Dr. Thorell has 
carried the formation of genera and subgenera too far, whilst the older system of Koch 
is entirely artificial and worthless. No writer on Scorpions has given consistently a 
clear statement or (what is more to be desired) good figures of the really important 
structural features of the genera, subgenera, and species proposed or recognized by him ; 
and it is with the object of pointing out what are the important points in which 
Scorpions may vary that the present remarks are published. It is impossible to deal 
with the genera of Ehrenberg and Leach. Starting with Koch, we find that he bases 
his system on the number and disposition of the lateral eyes, as follows :— 
, O 
SOU PUI. 5B 6 USE 6 eo << O 
° 
LRU ode oes Ice Oring 4 DRL fo) 
O 
TAU ;CUSS coe fo) 
fe) 
TEOUTA gs GORA Be aE @ 
Oo 
O 
UGVGONU Ss. ees 28 a O 
fe) 
yo [e) 
Sisyphus 5 
fe) 
S 
LTTIES ONCE, HCL CR ee, 
° 
eo 
Androctonus . male 
OS 
rl 
VoL, X1.—pParr x. No. 9.—May, 1885. 
