WATER BEETLES IN RELATION TO PONDFISH CULTURK. 



235 



how far they are able to overcome adverse conditions. It may also be extremely 

 useful in suggesting available food upon which they can be reared during experi- 

 mentation, but it does not indicate their natural food preference any more than a 

 prison menu indicates the preferences of a convict. The food of the species here 

 given is to be understood as the result of observations made in the ponds. What 

 they were known to eat in the laboratory is so stated and is included for the reasons 

 just given. 



Much also can be learned under artifical conditions about the methods em- 

 ployed by the different species in the construction of their pupal chambers; but 

 the distance they travel from the water's edge and the kind of a location they 

 choose can be judged only by finding the pupae in situ on the shore of the pond. 



The same is true of the materials used. There is no sand on the shores of any 

 of the ponds, and of more than 100 pupal chambers of Dineutes americanus col- 

 lected during the last three summers, every one was made of moist earth pellets. 

 Yet when six larvae, whose freshly made pupal chambers had been hopelessly broken, 

 were transferred to a suitable terrariimi and each constructed a new chamber, two 

 used entirely moist sand instead of earth pellets. The methods employed with 

 both materials were exactly the same, however. 



ECOLOGY. 



MODIFICATIONS OF STRUCTURE AND VESTITURE. 



All beetles that live in the water show some modifications of structure and 

 vestiture to fit them for their aquatic life. This fact was noted by Leng (1913, 

 p. 32) in a paper on aquatic Coleoptera in the Journal of the New York Entomo- 

 logical Society. He added that the modifications were more noticeable in the 

 adults than in the larvae. These modifications serve varied and quite different 

 uses and may be concerned with locomotion, with sex activity, with flotation, 

 with respiration, and with sight. They can be considered most conveniently in 

 connection with the various functions they assist. 



LOCOMOTION, 



The beetle larvae can all walk, but none of them move fast enough to warrant 

 the assertion that they run. Most of them can swim, and a few can jump; that is, 

 they can throw the body a short distance by kicking with the legs or by suddenly 

 flexing the posterior portion of the abdomen. The relative locomotor abflity of 

 the various larvae is given under each species separately. In general, the dytiscid 

 larvae are excellent walkers and swimmers, and some of them can jump. The two 

 species of Laccophilus are the best walkers and the most agile larvae of all those 

 studied, the two species of Thermonectes are the best jumpers, and the Cybister 

 larva is the most active swimmer. The hydrophflid larvae are fair walkers and 

 good swimmers, but none of them so far as known can jump. The gyrinid larvae 

 are good walkers and excellent swimmers, while the Dineutes larvae can jump, 

 although not as well as the Thermonectes larvae. The haliplid larvae can only 

 crawl, they can neither swim nor jump, and all their movements are extremely 



