I AQUATIC BEETLES 81 



which descended slowly and with great effort, until 

 apparently by the action of the basal joints of its legs 

 it dislodged a good-sized air-bubble. After this it 

 swam about freely. 



The antennae are used only for breathing by the 

 submerged Insect. Their place as feelers is sup- 

 plied by the long and forward-directed maxillary 

 palps. 



The food of the adult Hydrophilus is largely 

 vegetable, but it will prey upon small aquatic animals. 

 As some recent authors have said that the adult 

 Beetle feeds exclusively, or almost exclusively, on 

 animal substances, I may say that four Hydrophili, 

 kept in my aquarium, cleared it completely of small 

 weeds, devouring Nitella especially in large quantities, 

 and that in the absence of all animals bigger than 

 Daphnia they remained healthy and active. 



\Ye now resume Lyonnct's narrative : " I was 

 particularly anxious to ascertain how the females 

 constructed the floating cocoon which encloses their 

 eggs. For this purpose I placed a few of these 

 Insects with some Duckweed in a large wooden 

 trough on the last day of May. On the 1st of June 

 I saw that one of the females, contrary to its usual 

 custom, was incessantly swimming about, and search- 

 ing on all sides. I expected that this was because 

 she did not find materials suitable for her work, and 

 as I had often seen a filamentous alga attached to the 

 cocoon, it occurred to me to give her some of this. 

 I floated it on the water by means of wooden 

 shavings, and next day, the 3rd of June, I found the 

 beginning of a cocoon, but the Insect soon abandoned 



G 



