570 CLASS IX. 



class of the Crustacea occurs largely developed in Limulus. The 

 name of inner sternum has been given to it ; it occupies in some 

 degree the place of the entotliorax 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 1 . 



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 LINNAEUS) 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, TelypJionus 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. 



