PART III. LABORATORY EXERCISES 



CHAPTER XVI 



THE EXTERNAL ANATOMY OF THE LOCUST 



NOTE. Beyond a doubt, one of the most difficult problems every instructor in 

 the biological laboratory has to meet is to determine the amount of assistance 

 which shall be given individual students. In advanced work, probably the best 

 plan is to train students to rely on their own resources and to solve their own 

 problems. In elementary classes, however, far too much time is often wasted in 

 the laboratory because the instructor does not happen to be at hand to aid and 

 direct the student. For this reason the following instructions are given, more or 

 less in detail, with the hope that the students may intelligently carry on their 

 work without the constant attention of the instructor. 



In order to derive the most benefit from the laboratory work, it is essential 

 that the students should verify every detail of structure herein given before pro- 

 ceeding with the drawings, the latter being considered simply as a means to an 

 end. In fact, the amount of good derived by the student from the laboratory work 

 is largely dependent upon the energy of the individual. For this reason the lab- 

 oratory work should not be judged entirely by the drawings, and, if possible, the 

 actual amount of information obtained by the student in the laboratory should be 

 determined by examinations similar to those given in lecture or recitation work. 



For details concerning laboratory methods and equipment, see Chapter XXIII. 



SECTION I. EXTERNAL ANATOMY OF THE GRASSHOPPER (TYPE 

 OF CLASS INSECTA) 



Material. The red-legged locust (Melanoplus femnr-rubrum) has been 

 selected as the type of the class Insecta, partly on account of its abundance 

 and the ease with which it may be collected, and partly on account of its 

 simplicity of structure. Specimens for class work should be collected in the 

 late summer or early fall, and preserved in 85 per cent alcohol for three or four 

 days. After this time has elapsed, they should be transferred to 80 per cent 

 alcohol, to which 10 per cent of pure glycerin has been added. If soaked in 

 warm water a short time before using, the specimens will be rendered soft and 

 pliable. The students should verify the following points : 



1 . Body covering. Carefully examine with a hand lens the body 

 covering of the specimen, and note that it is made up of a series 



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