I AQUATIC BEETLES 83 



form the under side of the cocoon. The two curved 

 surfaces then were woven together, and the body of 

 the cocoon was finished, the work having occupied 

 about an hour and a quarter. For about two hours 

 after this the Beetle remained still, her back being 

 uppermost. At first her body was buried in the 

 cocoon up to the thorax, but one could now see that 

 she was gradually withdrawing it. During these two 

 hours of apparent rest she laid her eggs, not at hazard, 

 but in regular order, side by side, the pointed ends 

 uppermost. When the work had advanced so far 

 that her body was completely withdrawn from the 

 cocoon, she began to spin about the open mouth of 

 the cocoon, so as to gradually narrow the opening. 

 Then by spinning up and down she closed the end 

 of the cocoon, giving it a truncated appearance. The 

 next thing was to spin a little mast, which gradually 

 rose above the surface of the water, the fore part of 

 the Beetle during this part of the work being 

 constantly immersed. 



" I do not know the use of this little mast. Perhaps 

 it enables the Insect to get rid of an excess of silky 

 matter. However this may be, the work was com- 

 pleted in about five hours, after which the cocoon was 

 left floating. 



"On the 1 5th of July I observed an opening at the 

 foot of the mast, and saw, floating around, whitish 

 skins, either egg-shells, or the envelopes of the larvae. 

 Next day I saw a small larva emerge, and the day 

 after fifty more. From this point the history of the 

 Beetle has already been traced." 



More than fifty years after Lyonnet's observations 



G 2 



