ADJUSTMENT OF ORGANISMS TO EXVIROXMEXT 417 



representative. We may get some idea of the nature and 

 extent of the adaptative changes that have taken place with 

 the return to aquatic life, if we compare such a form as 

 Calosoma with one of the larger D^'tisicidae (fig. 244). 

 Something of the manner of life of the diving beetle has 

 already been seen in study 48. Calosoma is built for 

 running about on the ground, climbing in and out of depres- 

 sions, hiding in crevices; hence it is loosely jointed in both 

 body and legs, roughly contoured, with prominent eyes, and 

 large antennae beset with sensory hairs. In Coptotomus all 

 this is changed . The body is compact, rigid and pointed at 



the ends. The contour lines are 

 reduced to smooth curves. The 

 legs, especially the hind ones 

 that are chiefly used in swim- 

 ming are flat and oar like, com- 

 pacted and stiffened, limited in 

 variety and specialized in kind 

 of motion. Remote as is the 

 analogy, we may see some like 

 phenomena if we compare 

 vehicles for locomotion on land 

 with boats; especially, if we con- 

 ground beetle "trast the great variety of form of 

 sycophanta: after land vchiclcs with the great Uni- 

 formity in shape of hulls of boats. 



Fig. 246. A 

 (Calosofna 

 Bos). 



Study j^. A comparison of the structure of groiuid beetle afid 



diving beetle. 



Materials needed: A supply of specimens of one of the 

 larger Carabidae (Calosoma, Galerita, etc.), and of one of the 

 larger Dytiscidae (D3rtiscus, Cybister, Acilius, etc.). 



Let this study be a detailed examination of the external 

 structures, first of the ground beetle, and then of the diving 



