HOMARUS 167 



Order 3. Diplopoda. 



With numerous trunk segments, each with two 

 pairs of legs. No poison jaws. Body not com- 

 pressed. (Julus.) 



Order 4. Pauropoda. 



With ten trunk segments and nine pairs of legs. 

 (Pauropus.) 

 Class 5. Insecta. 



Body divided into head, thorax, and abdomen. 

 Three pairs of thoracic legs and generally one 

 or two pairs of wings. Some of the important 

 orders are: Thysanura, Orthoptera, Neurop- 

 tera, Hemiptera, Diptera, Lepidoptera, Cole- 

 optera and Hymenoptera. 



Brues and Melander: Classification of Insects. Bull. Mus. Comp. Zool., 

 73, 1932. 



Exner: Die Physiologie der facettierten Augen von Krebsen und In- 

 secten, 1891. See also Biol. Centr., 11, p. 581, 1891. 



Hilton: The Central Nervous System of Simple Crustacea. Jour. 

 Comp. Neur., v. 28, No. 2, 1917. 



Prentiss: The Otocyst of Decapod Crustacea: Its Structure, Develop- 

 ment, and Functions. Bull. Mus. Comp. Zool., Harvard, 36, 1901. 



Watase: On the Morphology of the Compound Eyes of Arthropods. 

 Stud. Biol. Lab. Johns Hopkins Univ., 4. 



CRUSTACEA 



HOMARUS AMERICANUS (Lobster 1 ) 



These animals are not generally found where they can be 

 readily observed in nature, but many valuable observations 

 can be made on specimens confined in aquaria. If other 

 animals are present in the aquarium notice the position of 

 defense that is taken. In nature the animal spends consider- 

 able time under rocks with the anterior end of the body 

 turned toward the opening. In this position both sense organs 

 and weapons are in the proper position for attack or defense. 

 Notice how the appendages are used. Are the sense organs 

 moved frequently? What is the advantage of having the 



1 These directions may be used for the crayfish without much modifi- 

 cation. The smaller size of these animals will make it more difficult 

 to trace some of the nerves and blood vessels. 



