1 68 



FIRST LESSONS IN ZOOLOGY 



inch to an inch and a half lonij. There are two principal 

 kinds, the jiredaceous diving-beetles, which kill and eat 

 other insects, and the water scavenger-beetles which feed 

 on decaying vegetation in the water. The first have slender 

 thread-like antenna;, while the second have antenna; 

 with thickened or club-like tips. As neither kind has 



Fii;. 124. — Pri<l,M_rnu- 'li\ in^-lic(.-Ll<'> (larj^c) and back•swimmcr^ in water. 

 (Slif,'litly Ic-is tliai] natural size; ilrawn from living specimens.) 



gills Ijfjth ha\'e to come to the surface to get air, but 

 they always carry down with them a supply sufficient to 

 last some time. The)- do this in two different -waj-s. 

 The predaceous diving-beetles force the posterior tip of 

 the body above the surfice (the)- al\\a\-s hang head 

 downward \\'hen at the surface) and slighth' lift the tips 

 of the horn\' black w ing-C()\'ers ^\hich lie on the back. 

 y\ir rushes in under the wing-covers and is held there by 

 the closing of the tips. The breathing pores or spiracles 



