The South Australian Naturalist. 



125 



No migrations of back-swimmers have been recorded in 

 Australia, but migrations en masse must occur, for myriads of 

 adults sometimes appear in dams, etc., which a day or two 

 before were destitute of l)ug life. In 1847 the migration of 

 a tremendous host of an American species Avas observed by 

 Sir George Simpson. The recorder of the occurrence says that 

 the bugs were suddenly incapacitated through encountering 



'ig. 1.— Anisops hyoerion, ventral view. Poising position as seen from 

 above when in the water. 



TWO ciiiiinoLis iiiemuers, facii uuii a saw-iiKC eage oi sironi? 

 teeth, and it is with these gouging gonapophyses that a recep- 

 tacle for the egg is prepared. An examination of the oviposi- 

 tor of other Australian members of the genus shows that it 

 is quite safe to assume that all of our species have the same 

 habit. 



