INSECTS 29 



strong hairs on the inner side. In swim- hairs, thus being doubly protected from 



ming the stroke is made by both legs at being wetted. At the moment the beetle 



once. Perhaps the most interesting facts reaches the surface, by a stroke of the 



about these beetles are those associated antenna (on the side which is nearest the 



with their method of breathing. surface, the body being tilted), the film 



The horny wing cases covering the ab- from the air space in which the antenna 

 domen are very thick and fit close against rests is carried upward and outward to 

 the abdomen, except at the extreme pos- the surface of the water, thus forming an 

 terior end of the body. The space be- opening to the exterior. By movements 

 tween the wing cases and the upper sur- of the wings, aided by bellows-like con- 

 face of the abdomen forms a large air tractions and expansions of the body, a 

 space. The spiracles, or openings into fresh supply of air is pumped into the air 

 the respiratory system, are situated at the reservoir. 



margins of the upper side of the abdo- In speaking of peculiar water insects 

 men. When the beetle comes to the sur- one must not forget to mention the larva 

 face for a fresh supply of air it exposes of Donacia. The adult female of this in- 

 the tip of the body and then by a depres- teresting leaf-eating beetle often cuts cir- 

 sion of the tip of the abdomen allows a cular holes in the large leaves of water- 

 fresh supply of air to enter into the cav- lilies, and. then deposits her eggs at the 

 ity below the wing covers ; this cavity is margin of these holes on the under side, 

 then closed and the beetle is ready for When the larvae hatch they make their 

 another trip under the water. When rest- way to the roots, upon which they feed, 

 ing in the water they float with their head The really remarkable thing about this 

 downward and the end of the abdomen larva is how it gets its air supply, as it 

 slightly projecting from the water; thus does not have gills, nor is it known to 

 a fresh supply of air is easy to secure. In visit the surface for a fresh supply of air, 

 their food habits these beetles are preda- and yet it has a normal air-breathing sys- 

 ceous, and in addition to other insects, tern. On the dorsal surface, near the tail 

 will even kill small fish. end of the body, are two slender, curved, 



The Water-scavenger beetles are not spine-like processes. The air tubes of the 



such perfect swimmers as the Predaceous body arise from the base of these spines, 



ones. When the latter makes a stroke in and spiracular-like openings are found at 



swimming it strikes with both hind legs, their base. 



while the Scavengers strike alternatingly Two different views have been advo- 



with the hind legs. Their method of se- cated to explain how it is possible for the 



curing and carrying air, as with other larva to secure air. There seems to be 



water-beetles, is remarkable. In addition no difference of opinion with regard to 



to the air reservoir under the wings, they the source of the air supply, from the air 



have on the under side of the body large cells in the root of the plant upon which 



hairy areas which communicate with the the. larva feeds. One view is that these 



one under the wings. All the air spaces air spaces in the plant are punctured by 



are thus in direct communication. The the spines and thus the air is taken di- 



respiratory openings in the Predaceous rectly into the air tubes. The other view 



water-beetles open on the upper side of is that the larva bites a hole into the air 



the abdomen, but in these beetles they are space and then, by the aid of the spines, 



on the lower side and surrounded by short holds the openings at the base of the spine 



hairs which preserve the air film on the against the air space and thus the air is 



lower surface. When the fresh air supply taken up. 



has been exhausted the beetle comes to The Back-swimmers are curious little 



the surface, tips the body slightly, so as fellows which swim upside down in the 



to bring the region on one side of the water, and by means of their sucking 



body just behind the head, to the surface. mouth parts, prey upon other small ani- 



The long antenna which is folded back- mals. The lightness of their bodies and 



ward and" reaches to the rear part of the the large amount of air which they carry 



head, occupies an air space in its apical with them make it necessary when they 



half, and in addition is covered bv fine wish to remain below the surface to hold 



