86 NATURAL HISTORY OF AQUATIC INSECTS CH. 



Miger observes that three kinds of secretions are 

 made use of by the Hydrophilus. There is first a 

 sticky liquid, which when drawn out into threads 

 makes them cling to one another, and forms a com- 

 pact though flexible envelope. Another fluid serves 

 to glue the eggs together, while the third forms a 

 silky shining tissue, like that of the cocoons of Lepi- 

 doptera. This tissue is well suited for the admission 

 of air, but when submerged it allows the passage of 

 water also. The eggs are regularly cemented together 

 side by side in a vertical position. The whole mass 

 of eggs is attached to the upper surface of the cocoon, 

 and has beneath it an air-space, which leads to the 

 opening by which the larvae emerge. This air-space 

 is only loosely closed by threads which are, however, 

 sufficient to prevent the entrance of the water. Since 

 the relatively heavy eggs are placed high in the 

 cocoon, and an air-space lies beneath, the cocoon 

 is liable to upset unless it is attached to a buoyant 

 body. 



As soon as the larvae are hatched, they swell out to 

 twice their previous size, free themselves from their 

 integuments, and escape into the lower part of the 

 cocoon, where for about twelve hours they move about, 

 one over another. 



Some additional particulars respecting the cocoon 

 of Hydrophilus are furnished by Mr. A. G. Laker.^ 

 He tells us that the average size is iih lines x lof 

 lines, and the height to the tip of the spike about 17 

 lines. The cocoons are buoyant, and when floating 

 freely about one third of their depth is out of water. 

 1 Entomologist, Vol. XIV. p. 82 (188 1). 



