306 



ZOOLOGY. 



CLASS II. PODOSTOMATA. 



Appendages of the cephalothorax in the form of legs, spiny at tht base ; 

 no antennae ; brain supplying nerves to the eyes alone ; nerves to the 

 .cephalothoracic appendages sent off from an wsophageal ring; nervous 

 system ensheathed by a ventral system of arteries ; metamorphosis slight, 

 flexes distinct. 



Order 1. Merostomata. No distinct thoracic segments and appendages. 

 (Limulus, Eurypterus.) 



Order 2. Trilobita. Numerous free thoracic segments and jointed ap- 

 pendages. (Agnostus, Paradoxides, Calymene, Trinucleus, 

 Asaphus; all extinct.) 



CLASSIFICATION OF THE ORDERS OF CRUSTACEA AND PODOSTOMATA. 



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1 



CRUSTACEA. 



PODOSTOMATA. 



Laboratory Work. In dissecting the lobster, the shell or crust may 

 be removed by a stout knife ; the whole dorsal portion of the cephalo- 

 thorax and each segment behind, including the base of the telson, 

 should be removed, care being taken not to injure the brain, which lies 

 just under the base of the rostrum. The hypodermis, or reddish, mem- 

 branous, inner layer of the integument, should then be dissected away, 

 exposing the heart, the stomach, the liver, and the large muscles of 

 the abdomen. The arterial system can be injected with carmine 



