I AQUATIC BEETLES 85 



Small bubbles of air were then seen to issue from 

 the cocoon. This was due to the displacement of the 

 contained air by eggs, which were laid side by side, 

 and glued together with a white liquid. In three 

 quarters of an hour the egg-laying was over. The 

 Beetle closed the cocoon slightly, and began to form 

 the pointed end. The wing-covers were now a little 

 opened, and their tips brought to the surface of the 

 water. The spinneret was uncovered, and its con- 

 tinuous and rapid movements could easily be followed. 

 The formation of the projection took more than half 

 an hour, at the end of which time the slender tapering 

 point rose about an inch above the water. The whole 

 operation took about three hours. 



Miger observes that at the beginning of the work 

 the Hydrophilus is easily disturbed, but when egg- 

 laying has once begun she may be removed from the 

 water, and her cocoon cut open with scissors without 

 creating a stoppage. 



He placed three females in a vessel of water with- 

 out any floating object. They were unable to form 

 a cocoon at all, though there passed from their 

 bodies a yellowish firm substance which contained 

 no eggs. 



The air which fills the cocoon is derived from the 

 supply carried down by the Beetle. The cocoon is 

 always fixed to a floating object. *' It is a mistake," 

 says Miger, " to suppose that the turned-up point of 

 the cocoon serves as a mast. Such a notion could 

 only be drawn from an empty cocoon. It is not 

 unlikely that the drawn-out point serves for the 

 supply of air to the cocoon." 



