CHAPTER XVII 



A COMPARISON OF THE DIFFERENT TYPES OF ARTHROPODA 



SECTION VI. COMPARISON OF INSECTS AND CRUSTACEANS 

 (TYPES, LOCUST AND CRAYFISH) 



Material. Alcoholic specimens of both crayfish and locusts should be pro- 

 vided, although the student by this time should be familiar with the structure 

 of the locust. The lobster is much larger and easier to work than the crayfish, 

 and instructions here given will apply to either. Both the lobster and the crayfish 

 may be obtained from any of the natural-history supply companies. Crayfish 

 may be collected in many sections of the country from streams and ponds, 

 and should be preserved in the same manner as recommended for the locust. 

 Material for Exercise 17 (the sow-bug) can be obtained in abundance under 

 boards and stones and in other damp locations. It may be preserved in 

 alcohol. 



Exercise 12. Comparison of the anatomy of the crayfish and the locust. 

 With the two specimens at hand, write out a careful comparison of the following 

 points: 



1. Nature of the body covering. 



2. General divisions of the body. (A fusion of the head and thorax is known 

 as the cephalothorax.) 



Exercise 13. The head and head appendages. Remove the appendages 

 from one side of the crayfish, beginning with the first appendage anterior to 

 the first walking leg. These may be removed by grasping them near their 

 attachment with a pair of strong forceps, and pulling them backwards toward 

 the posterior end of the body. As each one is removed, it should be laid on a 

 piece of wet blotting paper in regular order. The appendages of the crayfish 

 are numbered from the anterior to the posterior end of the body. The head 

 appendages are as follows : 



1 . The antennule, consisting of a basal piece and two long, slender filaments. 



2. The antenna, consisting of a basal piece, one long, slender filament, 

 known as the endopodite, and a short, platelike projection, known as the 

 exopodite. 



3. The mandibles. 



4. 5. The first and second maxillae. The above include all the head append- 

 ages. Write out a careful comparison of these appendages and corresponding 

 appendages in the locust. Also with a hand lens make a comparative study 

 of the eyes. 



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