THE NOTONECTID^. 139 



but instead of being in y^on^ of the eye, they are placed 

 in a hollow beneath it, similar to the FlatidcB. Such 

 are the primary^ or typical, characters of this family ; 

 but to attempt the definition of all those intervening 

 links by which it is connected with the preceding, would 

 far exceed our limits. There are several small groups, 

 peculiar to India and Australia, to which Nature has 

 obviously assigned an intervening station ; for all her 

 paces are slow and measured : if they appear otherwise, 

 as they certainly do in some few instances, we must set 

 it down to our own ignorance of her productions, rather 

 than to her departure from her usual principle of gra- 

 dual developement. 



(127.) The fourth family of this tribe appears com- 

 posed of the NoTONECTiD^, or boat flies, constituting the 

 natatorial or swimming type of the whole group. Our 

 reasons for including these insects in this tribe, rather 

 than in the last, cannot be entered upon in this place. 

 It will be sufficient if the reader is made acquainted with 

 the general form of these insects, and their peculiar ha- 

 bits. For this purpose, let him fancy that a minute 

 insect, whose shape immediately reminds him of the 

 British Centronotus GenistcB, but whose hinder feet are 

 formed for swimming, he will thus liave a very good 

 idea of the general form of the boat flies ; and more 

 especially of the genus Ploa, or the minute Sigara of 

 Dr. Leach. Without touching upon their other pecu- 

 liarities, it will be sufficient to state that the Notonec- 

 tidce are immediately known by their long hinder legs, 

 the tarsi of which are so compressed and fringed as to 

 resemble oars ; these enable the insect to swim with 

 great rapidity. The shape of the body is thick and tri- 

 angular ; and the outer half of the superior wings fold 

 over each other. Dr. Leach very properly divides this 

 family into two groups ; one (^Notonectu) having the 

 shield {scutcUum) large; the other, as in Corixa, being 

 entirely without this part. On a fine summer's day, 

 they may be observed basking in the sun, close to the 

 surface of the water, in clear ponds or ditches; here 



