HYDROPHILUS PICEUS AND HYDROBIUS FUSCIPES. 83 



a floating aquatic leaf; and in the latter case the spike has always 

 protruded beyond the edge of the leaf, but the cocoon itself has 

 been hidden from above, but it would of course have been con- 

 spicuous from beneath the surface of the water. 



It seems reasonable to suppose that the long spike with which 

 these cocoons are furnished should perform some definite office, 

 but I have been unable to determine what it is. Tlie 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 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 uppermost, 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 only partially submerged and then released, the 

 cocoon turns bottom upwards. 



The number of eggs contained in each nest is usually between 

 50 and 60 ; thus in four cocoons, of which I counted the larvae 

 when they emerged, the figures were respectively 53, 57, 56, and 

 57, or an average of 56. It will be observed how closely these 

 figures approximate. 



The egg-pouches made by Hydrohius fuscipes are very similar 

 in substance and general appearance to those of Hydrophilus 

 piceus, although far smaller, being about the size of a pea, 

 flattened on one side, and are without any spike. I have found 

 them very plentiful in April and May, attached to the under side 

 of floating grass, their presence being indicated by the upper 

 side of the grass leaves having small patches or streaks of white. 



