570 CLASS IX. 
class of the crustacea occurs largely developed in Limulus. The 
name of inner sternwm has been given to it; it occupies in some 
degree the place of the entothorax in insects, is not however a 
horny part penetrating inwards from the integument, but a pro- 
duction from the numerous interwoven tendons of the different 
muscles which mutually meet there?. 
Arachnids are met with in every quarter of the globe. I am 
acquainted with no families or principal groups (larger genera in the 
sense of Linnamus) which, as is the case in other classes, belong 
exclusively to the eastern or the western hemisphere. The larger 
arachnids inhabit warm regions, especially the genera Scorpio, 
Mygale, Telyphonus and Phrynus. By far the most of the animals 
of this class live on land, others in fresh water, in the sea only very 
few, just the reverse of what we remark in the crustaceans. 
1 A similar part is the linea alba, for the abdominal muscles of mammals. 
