86 



NATURAL HISTORY OF ARTHROPODS. 



Limulus lives upon the many small animals which it finds in the mud, worms forming 

 the bulk of its diet. It grasps the food by one or more of its numerous pincers, and 

 places it between the spiny basal joints of the legs, which are kept in constant motion 

 rasping the food into minute particles and forcing them into the mouth. 



The horseshoe crab, like other Arthropoda, allows for increase in size by moulting. 

 The hardened integument of the cephalothorax splits along the sharp margin, and 

 through the opening thus afforded the animal extracts himself, leaving even the lining 

 of the anterior and posterior portions of the digestive canal behind. 



Like many other types of animals which have existed on the earth through many geo- 

 logical periods, the horseshoe crab has great vitality. Not only can it bear immersion in 

 fresh water for several days, or even a complete removal from any aqueous element for 

 the same length of time, but its eggs are laid in the sand, where they are twice a day left 

 uncovered by the retreating tide, and are exposed to the fresh water of the frequent 

 rains of spring. 



SUB-ORDER I. - - POECILOPODA. 



Limulus and its nearest fossil allies are united into a sub-order under the above 

 name. Of the living species of Limulus we have already spoken above. The genus 

 makes its appearance in the lithographic slates of Solenhofen, Bavaria, which are of 

 Jurassic age. Prestwichia and Euproops are found in the carboniferous rocks of Illi- 

 nois. In their general appearance they differ but little from the Limulus of to-day. 



SUB-ORDER II. - - EURYPTERIDA. 



The animals which are associated together under the sub-ordinal name Eurypterida 



appear in the upper Silurian, 

 and become extinct in the 

 carboniferous. In general ap- 

 pearance they are intermedi- 

 ate between the king-crab 

 and the scorpions. To the 

 anterior portion of the body, 

 which we may call the cephal- 

 othorax, are attached at the 

 most but five pairs of limbs 

 which, like those of Limulus, 

 have spines on the basal joints. 

 One or more of the anterior 

 pairs may terminate in a pin- 

 cer, while the posterior pair 

 are usually expanded so as to 

 form a broad paddle. A met- 

 astoma is present, occupying 

 the same place as that of Lim- 

 ulus. On the upper surface 

 are the two eyes. The ab- 

 domen is large and long, 



FIG. 119. Eurypterus remipes, reduced. A, dorsal, and B, ventral view. and is Composed of twelve 



Meta8toma - ^ Cephalothorax. , 



