ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 415 



Arrangement (solitary, in clusters, in whorls, etc.; give 

 number) . 



f as to movement (stagnant, quiet, rapid, torren- 

 Water < tial, etc.) 



( as to oxygen content. 



The record of this study will be contained in the completed 

 table. 



2. Pkylo genetic adaptation in diving beetles. 



We will now study 

 the adaptation to a 

 changed environment of 

 a series of forms of com- 

 mon origin. For that 

 purpose it would be hard 

 to find better material 

 than that furnished by 

 the family Dytiscidae of 

 diving beetles (fig. 244). 

 Almost any permanent 

 pond will furnish a num- 

 ber of forms that differ 

 in size and habit, and 

 that exhibit different 

 degrees and kinds of 

 specialization. We will 

 study the adaptation of the adult beetles to pond life. 



These beetles have fully retained their terrestrial mode 

 of respiration. They take in air through abdominal 

 spiracles situated on the back of the abdomen, underneath 

 the wing covers. They have merely adopted improved 

 means of carrying air with them when they descend beneath 

 the surface of the water. 



FIG. 244. A diving 

 inter rogatus). 



beetle (Coptotomus 



