Ephemeroptera 267 



it is usually possible to locate numbers of males and females dancing up 

 and down in their mating flight near the bank of a pond, lake, or stream. 

 One by one the females leave the throng and fly over the water, here and 

 there dropping with their eggs to the surface. With a net capture one 

 of these females before she reaches the water. Holding her gently by 

 the wings wash the eggs into a culture dish and transfer them to the 

 laboratory.* 



Mayflies of the genus Baetis do not carry their eggs in a protruding 

 mass, but crawl into the water and lay them in a flat layer on a sub- 

 merged stone. These may be removed with a scalpel as soon as laid and 

 carried to the laboratory in water. 



With the aid of a lens and a scalpel, separate individual eggs and trans- 

 fer them to culture dishes by means of a medicinal pipette. Covered 

 culture dishes 75 mm. x 20 mm. prove very satisfactory. Fill each dish 

 % full with tap water seasoned for 24 hours in an open container at room 

 temperature. With a pipette change half of the water every three days. 

 Avoid sudden temperature changes. 



Diatoms and desmids freshly scraped from stones from a stream 

 furnish excellent food. One drop of thick culture every three days is 

 sufficient for a very young nymph. Twice that amount is required later. 

 Diet may be varied by the addition of a small fragment of Spirogyra. 



When longitudinal venation is clearly evident in the wing pads prepare 

 for emergence. Cut a piece of No. 12 or No. 16 wire cloth 12 cm. x 30 cm. 

 Remove the glass cover and roll the wire to fit tightly inside the glass 

 rim. Pinch the top together and fold twice, making a closed seam. This 

 cage allows the specimen to crawl from the water and to hang in the 

 air waiting for the final molt. 



In Baetis vagans there are 27 instars and 6 months are required for 

 the development of the summer brood. 



Bibliography 



Murphy, Helen E. 1922. Notes on the biology of some of our North American 



mayflies. Lloyd Library Bull. No. 22. 

 Smith, O. R. 1935. Eggs and egg-laying habits of North American mayflies. In 



Needham, Traver, and Hsu: The Biology of Mayflies, p. 67. 



* Editor's Note: Artificial fertilization of certain mayflies (Hexagenia, Ephemera, etc. ) 

 is easily effected by mixing freshly liberated eggs and sperms in a watch glass of lake water. 

 A gravid female taken in her ovipositing flight will shed all her eggs with the greatest 

 readiness on such stimulation as snipping off her head or subjecting her to tobacco fumes. 

 Eggs of a subimago are sometimes mature and ready for fertilization. J. G. N. 



