306 



ZOOLOGY. 



Class II.— PODOSTOMATA. 



Appendages of tJie eephalofhorax in the fmm of legK, spiny at the base; 

 no antennm; brain supplying nerves to the eyes alone; nerves to tlie 

 cephaloihoracic appendages sent off from an asopliageal ring; nervous 

 system ensheathed by a ventral system of arteries ; metwmorplwsis slight. 

 Sexes distinct. 



X)rder 1. Merostomata. — No distinct thoracic segments and appendages. 

 (Limulus, Eurypterus.) 



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

 pendages. (Agnostus, Paradoxides, Calymene, Trinucleus, 

 Asaphus; all extinct.) 



Classification of the Orders of Crustacea and Podostomata. 







a 

 I? 



I 



t 



6 



s 



IS 



!^ 



Crustacea. 



u 



Podostomata. 



Laboratoi-y Work. — In dissecting the lobster, the shell or crust may 

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

 fhorax 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 



