134 



HALF HOUES WITH INSECTS. 



[Packard. 



very few insects live in salt water, and it is easy to see that 

 a maritime life is not a normal one to them. So in a less 

 degree with the fresh water forms. The aquatic insects are 

 representatives of scattered families, and though all are in 

 various ways modified by their aquatic surroundings, 3-et so 

 much do they differ in their modes of development and 

 structure among themselves, that it is easy to see that they 

 belong mainly to terrestrial types which have adopted an 

 aquatic life after the t3'pe to Avhich they had belonged had 

 become fixedly terrestrial. For example, many beetles 



¥lG. 94. 



Fia. 95. 



Fig. 90. 



Dytiscus. 



A Carabid. 



Amphizoa. 



which are aquatic are allied to the carnivorous ground 

 beetles. The Dytiscus and its allies are essentially aquatic 

 Carabidfe, the family comprising the ground beetles. The 

 larvffi of these water beetles have the same kind of feelers 

 and mouth-parts as the land Carabids ; the structure of the 

 adult beetle is on the Carabid type, the body being, how- 

 ever, more ovate and modified for swimming. Both types 

 (Figs. 94 and 95) may have been derived from ancestors 

 of terrestrial habits. As proof of this we have the Cali- 

 fornian Amphizoa (Fig. 96), which is said by Dr. Horn to 



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