41 8 GENERAL BIOLOGY 



beetle, omitting mouth parts which are little altered in rela- 

 tion to aquatic life. All the hard parts (sclerites) of the body- 

 armor may be identified with the aid of figure 245. 



The purpose of the study is the gaining of some notion of 

 what are primitive and what are specialized conditions in 

 diving beetles. 



Study the structure of the diving beetle especially with 

 reference to : 



i) That fitting together of the ventral sclerites of the 

 thorax that has to do with increasing the rigidity of the 

 body. 



2) That fitting together of wing covers with each other 

 and with the sides of thorax and abdomen that has to do 

 with making a secure enclosure for the retention of air when 

 at the bottom of the pond. 



3) That consolidation and alteration in form of the hind 

 coxae that has to do with increasing the rowing efficiency of 

 the hind legs. 



The record of this study may consist of a brief tabular 

 statement of the chief structural differences between the 

 two beetles examined, illustrated with diagrams if desired. 



Study j6. A comparative study of size and activities of 



diving beetles. 



Materials needed: Plenty of live specimens representing 

 six or more genera of Dytiscidae, preferably of different 

 sizes. The specimens should be in normal condition ; if not 

 freshly collected, they should have been properly kept, cared 

 for and fed. 



Prepare a table with the following column headings 

 abbreviated as desired: 



Name (if unknown, use the keys and figures provided in 

 the appendix). 



