398 Annals Entomological Society of America [Vol. VI, 



other actual determination of the fecundity of May-flies since 

 that time. 



In this study the eggs of seventeen May-flies have been 

 counted and examined. They were taken from imagos which 

 had been kept in cages until they showed signs of old age. 

 Usually a count was made of the eggs in several individuals 

 and an average taken. They were examined and counted 

 upon a glass slide in a mixture of water and glycerine which 

 formed a convenient medium in which to manipulate them. 

 The results of the counting are given in a table which follows. 



All of the eggs are viscid. When laid in dishes they ad- 

 here to the bottom, as do those of Bsetis to stones. When 

 twigs or algae are introduced, they become attached to them. 

 There are two kinds of structures found upon them ; micropylar 

 structures and knob or thread-like extensions of the chorion, 

 both of which are important to the egg; and there is also a 

 variety of chorionic sculpturings which have no apparent 

 significance. 



Examples of the more important structures were long 

 ago pointed out. Polar knobs (micropylar structures) were 

 figured by Burmeister '48, and described by Leuckart '55. 

 The latter believed that the knobs were composed of masses 

 of spermatozoa and it remained for Grenacher, '68, to find 

 many stages of them upon developing eggs in the egg-tubes 

 and to point out their true nature. Micropylar structures 

 w^ere also shown in Palingenia virgo by Joly, '71 and '76, 

 and in Bastis sulphurea by Joly, '76. Grenacher, '68, also 

 pointed out (upon an unnamed May-fly egg) some little threads 

 "which were continuous with the chorion and which bore tiny 

 spheres upon the ends. He figured these with remarkable 

 accuracy. Of the eggs here figured, three bear a micropylar 

 apparatus, five have thread-like extensions of the chorion 

 and nearly all are more or less elaborately sculptured. 



The eggs of closely related forms may be very different. 

 This is well shown by a comparison of those of Ephemerella 

 excrucians and E. rotunda (PI. LIV, Figs, 66, 67). The 

 eggs of Ephefnerella excrucians are pure white, and slightly 

 dumb-bell shaped, with a disftinctly sculptured chorion, but 

 with no micropylar apparatus. Those of Ephemerella rotunda 

 are yellowish and oval with a prominent mushroom shaped 

 cap about the micropyle. If examined in the body or when 

 first extruded, two small knobs may be seen upon either side 

 of the egg, near its lower pole. Each knob is attached to the 



