IV AQUATIC CATERPILLARS 233 



which it holds on, being motionless. The movement 

 lasts for twenty seconds. At these times the filaments 

 are depressed and pointed forwards, instead of radiat- 

 ing as usual. All the segments, except the second, 

 third and last, carry black spiracles, those of the 

 second, third and fourth abdominal segments being 

 much larger than the rest. The spiracles are not 

 however open, and are functionless. De Geer imitated 

 Reaumur's experiment of oiling the stigmata. The 

 result was very different in the case of Paraponyx ; 

 one larva when immersed in olive oil lived eight days, 

 and spun against the side of the vessel. 



The Insect passes the winter as a larva, and in 

 captivity at least, feeds the whole time. In June De 

 Geer observed that cocoons were formed between the 

 young leaves of Stratiotes, well below the surface of 

 the water. The cocoon is grey outside, but lined with 

 close white silk. A large opening is left in the outer 

 envelope of grey silk, whose function is uncertain. 

 De Geer thinks that it may serve for the escape of 

 the Moth, or else for allowing free access of water. 

 The pupa has three pairs of prominent spiracles. It 

 is submerged, but the cocoon which it inhabits is 

 filled with air. Pupae removed from the cocoon, and 

 placed in saucers of water, lived for several days, 

 but ultimately perished without producing Moths. 

 Others when taken out of the cocoon and placed in 

 air, perished quickly. Others again, when placed 

 with one side of their bodies in water and the other 

 side in the air, survived, and produced Moths. These 

 facts appear to indicate that the stigmata are actually 

 employed by the pupa for respiration. As the cocoon 



