1913] Biology of May-flies. 399 



distal end of a thread-like extension of the chorion, which 

 lies beneath it, tightly coiled like a watch spring. Upon 

 coming in contact with the water these threads spring out 

 like elaters. The little knobs thus extended probably act 

 as floats or anchors for the egg. An even greater difference 

 between the eggs of closely related forms may be seen in the 

 eggs of Heptagenia interpunctata (PI. LIII, Fig. 65) and Hep- 

 tagenia pulchella (Fig. 64). The former has a pure white 

 oval egg without sculpturings or extentions of any kind. The 

 latter is white and slightly rounder with small regularly ar- 

 ranged bosses upon the chorion. At each pole there is a skein 

 of fine bright yellow thread. These skeins are also prominent 

 upon the poles of developing eggs, even in the tips of the 

 egg-tubes. Upon a glass slide they are easily seen with the 

 naked eye and the threads may be pulled out with needles 

 to a length of two or three inches. As soon as the eggs float 

 free in water the skeins begin to unroll and if shaken a little 

 they quickly uncoil altogether and become entangled with 

 any object near them. In nature the eggs are deposited 

 upon the surface of moving water. The threads just described 

 probably wind about sticks or plants and thus anchor the 

 eggs and keep them from being buried with silt during incu- 

 bation. 



Similar extensions of the chorion are found upon the eggs 

 of Tricorythus allectus and Ecdyurus maculipennis. The 

 eggs of Tricorythus (PL LII, Fig. 60) are bright green and 

 oval with a prominent shingle-like surface. Upon each side 

 of the egg toward the lower pole are two threads very similar 

 to those of Ephemerella rotunda, but without any knobs 

 upon the ends. At the other pole is a prominent smooth 

 yellowish micropylar apparatus. The eggs of Ecdyurus (PI. 

 LIII, Fig. 62) are roundly ovate and pure white. Their entire 

 surface is covered with minute pits and scattered between 

 these are numerous short blunt projections. When the egg 

 is first removed from the body, a small coil of thread -may 

 be seen in the depression on the top of each projection. As 

 soon as the egg has been in the water a little while, each coil 

 unwinds with a sudden spring. At the end of each thread 

 is a tiny viscid button. 



The eggs of Leptophlebia sp.? (PI. LII, Fig. 58) are elongate 

 ovoid, distinctly brownish and thickly covered with short 

 hairs, so that they look like ciliated protozoans. Those of 

 Choroterpjes basalis (PL LIII, Fig. 63) which are laid in the same 



