156 ARTHROPOD A. 



Order 8. Hymenoptera. 



Metamorphosis indirect. Two pairs of membra- 

 nous wings. Mouth-parts suctorial and man- 

 dibulate. (Apis, Vespa.) 



Exner: Die Physiologie der facettirten Augen von Krebsen und Insecten, 



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, Development, 



and Functions. Bui. 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. (Lobstef.i) 



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 probably spends considerable 

 time under rocks with the anterior end of the body turned to- 

 ward 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 fre- 

 quently? What is the advantage of having the eyes on stalks? 

 What appendages are used in walking? Are all of these ap- 

 pendages used in just the same way? Does the animal move 

 equally well in all directions? Perhaps you can make the animal 

 swim; if so, observe the method. Feed a specimen with por- 

 tions of a clam or fish, and see how food is torn to pieces and 

 transferred to the mouth, and determine, if possible, how the 

 mouth appendages are used. 



Appendages may be missing. If any are, notice at what 

 point they are broken. Possibly small appendages may be 

 growing from the old stubs. Autotomy may be studied by 

 crushing a claw or a leg of the fiddler crab, Uca. Other forms 



^ 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. 



