326 



ZOOLOGY. 



Zoea. Suborder 1. Cumacea (Cuma). Suborder 2. Schiz- 

 opoda(M.ys\s). Suborder 3. Macrura (Crangon, Astacus, Ho- 

 marus). Suborder 4. Braehyura (Cancer). 



Subclass 2. Pal&ocarida. Appendages of the cephalo-thorax in the form 

 of legs, ratlier than jaws ; no antennae ; brain supplying 

 nerves to the eyes alone ; nerves to the cephalo-thoracic ap- 

 pendages sent off from an cesophageal ring ; nervous system 

 ensheathed by a ventral system of arteries; metamorphosis 

 slight. Sexes distinct. 



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

 (Limulus, Eurypterus.) 



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

 pendages. (Aguostus, Paradoxides, Calymene, Trinucleus, 

 Asaphus ; all extinct.) 



CLASSIFICATION OF THE SUBCLASSES AND ORDERS OF CRUSTACEA. 







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NEOCARIDA. 



PAL^EOCARIDA. 



CRUSTACEA. 



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, 



