I AQUATIC BEETLES 87 



They are usually but not always attached to long 

 grass or floating leaves. " The spike consists of a 

 substance somewhat thicker and stronger than the 

 rest of the cocoon, and is hollow throughout the 

 greater part of its length, except that it is crossed 

 and recrossed inside with a dark thread-like substance, 

 thus somewhat resembling a horn stuffed with tow. 

 The apex of the spike does not, however, appear to 

 terminate in an orifice, but is closed. It does not 

 seem to me that this spike can serve as a balance to 

 the cocoon, because the nests are usually attached to 

 some kind of support. I may, however, mention that 

 I cut off the spike from two of the cocoons, and in 

 both these cases the eggs did not hatch ; it is, however, 

 possible that this may have arisen from some other 

 cause, although these particular cocoons appeared to 

 be similar in every respect to others of which the 

 eggs matured in due course. The cocoons from 

 which the spikes were removed subsequently sank. 

 These nests are so constructed that when floating 

 loose the spike retains its proper position, and even 

 if the cocoon be held so that the spike is parallel with 

 the water, and then suddenly released, it immediately 

 rights itself; if, however, the spike be partially sub- 

 merged and then released, the cocoon turns bottom 

 upwards. The number of eggs contained in each nest 

 is usually between fifty and sixty." 



Hydrobius. 



In shallow, grassy ponds there may commonly be 

 found a little blackish Beetle, about a quarter of an 



