VIII BELOSTOMIDAE NOTONECTIDAE CORIXIDAE 567 



know how they are charged. Another extremely interesting 

 analogy is found in the manner in which the elytra are locked 

 to the body ; a projection from the thoracic side-pieces, forming 

 a long pouch, into which a fold on the inner side of the elytra 

 fits, the two being subsequently locked by the action of some 

 special projections. This arrangement is similar to that which 

 exists in the anomalous family of water-beetles Pelobiidae. In 

 order to make this mechanism more perfect the side-pieces in 

 Belostoma form free processes. Martin has informed us that the 

 young have the metasternal episteruum prolonged to form a 

 lamella that he thinks may be for respiratory purposes.^ About 

 twelve genera and upwards of fifty species of Belostomidae are 

 known. None exist in our isles, but several species extend their 

 range to Southern Europe. In the waters of the warm regions of 

 the continents of both the Old and New Worlds they are common 

 Insects, but as yet they have not been found in Australia. 



Fam. 24. Notonectidae. — Prosternum short, so that the legs 

 are placed near th e lack part of it as well as near the front ; hack 

 of the head overlapped hy the front of the p)ronotutn. — The water- 

 boatmen are extremely common in our ponds, where they may 

 be seen rising to the surface and raising the posterior extremity 

 of the body for breathing. They swim on their backs instead of 

 in the usual position, and have an elaborate arrangement of long 

 hairs on the body to assist them to carry about an air-supply. 

 They are said to be lighter than the water, and to have some 

 difficulty in keeping away from the surface. Notonecta glauca 

 is the only British species, but we have a second minute Insect, 

 Plea viinutissima, belonging to the family. It lies in the mud at 

 the bottom of shallow waters, and may sometimes be fished up in 

 great numbers. It is considered by some authors to form a 

 distinct family. The oviposition of Notonecta has been observed 

 by Eegimbart ; the eggs are inserted into the stems of aquatic 

 plants. 



Fam. 25. Corixidae. — Prosternum short, as in Kotonectidae ; 

 summit of the head free from tlie thorax. — We have numerous 

 species of the genus Corixa in Britain ; and others extremely 

 similar in appearance occur in various parts of the world. The 

 head is remarkably free, and capable of great rotation. On 

 dissection it is found to be attached to the thorax only by a 



^ Bull. Mus. Paris, 1896, p. 238. 



