306 



ZOOLOGY. 



Class IL— POBOSTOMATA. 



Appendages of the eephaZothorax in tfie form of leg», spiny at the base ; 

 ■no antenruB ; brain supplying nerces to the eyes alone; nenes io the 

 cephaloihoraeie appendages sent off from an (esophageal ring ; nervous 

 system ensheathed by a -central system of arteries ; metamorpliosis slight. 

 .S'cj:«s distinct. 



Order 1. Merostomaia.—^o distinct thoracic segments and appendages. 

 (Limulns, Etuypterus.) 



Order 2. TrUdbiia. — Numerous free thoracic segments and jointed ap- 

 pendages. (Agnostus, Paradoxides, Calymene, Trinuclens, 

 Asaphus; all extinct.) 



Classification of the Osdebs of Crustacea, aot) Podostosiata, 



^ I 



i 





8 



^ 

 S 



Crttstacea. 



PODOSTOilATA. 



Laboratory Work. — In dissecting the lobster, the sheU or crust miy 

 l)e removed by a stoul knife ; the whole dorsal portion of the cephalv 

 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 o! the rostrum. The hyjxxiennis, or reddish, mem- 

 branous, inner layer of the integument, should then be dis.sected away, 

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

 the abdomen. The arterial system can be injected with carmine 



