136 



LEAVES FROM MY NOTE-BOOK. 



hairs keep free from water ; these spaces are filled with atmos- 

 pheric air, which the beetle drinks in energetically, remaining for 

 that purpose at the surface of the water. 



The female of Hydrophilus constructs a neat cocoon, shaped 

 somewhat like a coracle, containing about a hundred eggs, 

 and to her cocoon she adds a mast, which appears to serve the 

 purpose of steadying the small structure. If the mast be cut off, 

 the cocoon sinks ; if it be partially submerged, the cocoon turns 

 bottom upwards. The cocoon is always moored to some floating 

 weed, and the naturalist, Miger, had the good fortune to watch 

 the whole process of the construction of one (Fig. 4). The larva 

 of the small yellow fly, Dixa^ employs the surface film to buoy up 

 its head and tail ; its body being bent into a V* the apex of which 



Fig. 4. — Cocoon of Hydrophilus. 

 A shows the mast. B is opened to expose the eggs. From Miger. 



travels foremost, each half of the V alternately shoving the body 

 forwards. At the tail end is a respiratory cup, furnished with 

 valves, flaps, and outstanding processes, all fringed with long hairs, 

 which serve to exclude the water from a shallow, sunk space, upon 

 which the longitudinal tracheal trunks open. If the larva should 

 slip into deep water, the respiratory cup remains free from water, 

 and buoys up the tail. If the whole body is sunk below the sur- 

 face, a bubble of air is carried down enclosed in the fringes of 

 the respiratory cup. The larva, when thus submerged, swims 

 energetically, and can readily regain the surface of the water. 



The larva of the aquatic fly, Dicranota, has elaborate con- 

 trivances for hunting its favourite prey, Tiibifex^ a small red worm, 

 to be found at the bottom of muddy pools and slow streams. 



