SECRETARY'S REPORT. 143 



The genera Treclins of Clairville, Bembidiuni of Illijj:cr, and 

 Ochlhedromus of Leconte, are coniiuonly represented here by 

 quite small species, many of them marked with light or metallic 

 spots ; some of them feed upon dead animal matter as well as 

 upon other insects, and although scarcely averaging .1 in length, 

 have been known to attack and destroy an insect of five or six 

 times their bulk. 



In the natural classification of insects, so far as modern 

 investigations have been able to prove, we next come to a large 

 group living almost entirely in or upon the water, some pre- 

 ferring the muddy bottoms of half stagnant ponds, others the 

 surface of clear, running streams. This group is divided into 

 two families, the Dytiscidcc, and the Gyrinidce of Linna3us. 

 The former, derived from the Greek dytes, signifying a diver, 

 and the latter from g'ljros, signifying a circle, in allusion to 

 the peculiar habits of this family in gliding round and round on 

 the surface. They are all insectivorous, both in the larva and 

 imago state, but as they feed chiefly on the insects inhabiting 

 the water which are either similar in their food and habits to 

 their destroyers, or devour only water plants of no value to the 

 agriculturist, they can hardly be considered as among the 

 most serviceable of the insect tribes. They frequently seize, 

 however, on noxious insects which fall into the water by 

 accident, and would otherwise escape. The Gi/rinidce, com- 

 monly called " whirligig-beetles," are seen during the summer 

 months circling round, and darting swiftly in various directions 

 on the surface of almost every pool or rivulet. They are all of 

 a broad, oval form, generally of a polished black, with broad, 

 oar-like hind tarsi and long slender fore-feet, used in seizing 

 their prey, and have a singular smell, somewhat like that of 

 over-ripe apples when taken in the fingers, which proceeds from 

 a milky fluid secreted by them. They are of various sizes, 

 measuring from less than .2 of an inch to considerably over 

 lialf an inch in length. They occasionally migrate from one 

 pool to another, generally flying during the night, when they may 

 often be attracted by a light ; they are frequently picked from 

 the glass tops of green-houses or hot beds, on which, mistaking 

 the surface for water, they have dropped with such force as to 

 stun or kill them. Figure 19 represents one of our commonest 



