CLASS ARACHNIDA. 



57 



ORDER MEROSTOMATA (me ro stom'a ta). 



The Horse-shoe, or King- 

 crab, is found on the salt flats 

 of the Atlantic coast. It is 

 provided with a pair of simple 

 and a pair of compound eyes, 

 and has the head and thorax 

 united into a single broad 

 rounded lobe ; this bears below 

 it, six pairs of appendages, the 

 bases of which, armed with 

 in-pointing spines, force the 

 food into the mouth. The ab- 

 domen is smaller, and below 

 it, attached to five of the six 

 pairs of flattened appendages, 

 is a series of gills.* 



FIG. 89. 



Lim' u lus pol y phe'mus. Horse-shoe Crab. 

 Under Surface. 



CLASS ABACHNIDA (a rak'ni da). 



The Mites, Scorpions, and Spiders, are provided with 

 simple eyes only, though they resemble the Horse-shoe 

 in not having the head distinct from the thorax, in 

 being destitute of antennae, and in having six cephalo- 

 thoracic appendages. 



ORDER ACARINA (a ka rT'na). 



The Mites and Ticks are often degenerate forms, being 

 chiefly parasitic (par a slt'lk). The mouth parts are formed 

 for sucking, either vegetable , or animal juices, and the 

 segmentation of the body is more or less obscured. The 



* The TrilobUes (trl'lo bits), which figure so largely in Paleozoic (paleozo'ik) 

 Geology, present many points of structure in common with the King-crab. 



