7 8 Invertebrate Zoology. 



THE LOBSTER 1 



{Homarus americanus}. 



External Anatomy. Is the animal perfectly " bilater- 

 ally symmetrical " ? What characters distinguish the anterior 

 portion of the animal from the posterior? It will be ob- 

 served that the latter, the abdomen, is segmented. Look 

 carefully and see if there are traces of segmentation in the 

 anterior portion, the cephalothorax. Is the number of ab- 

 dominal segments constant? 



Has each abdominal segment a pair of appendages ? Do 

 they all take their origin from similar points of the several 

 segments? The ventral piece lying between each pair of 

 appendages is called the sternum. The dorsal portion is 

 the tergitm. The ventrally projecting lateral lobes are the 

 pleurons. The epimeron is a piece, more clearly seen on the 

 first abdominal segment, that lies ventrally between the ap- 

 pendage and the pleuron. Note any specialization of any 



1 The lobster has been here introduced for several reasons. Its gen- 

 eralized structure, large size, and the easiness with which its organs may 

 be dissected make it a most convenient animal for the demonstration 

 of not only arthropod morphology, but of general Invertebrate anatomy. 

 It is, moreover, a typical crustacean, and in a shorter course might be 

 studied as a representative of the entire Class. The Crustacea considered 

 farther on are especially valuable for comparative study. 



