400 



Annals Entomological Society of America [Vol. VI, 



or similar situations have no extensions of the chorion. They 

 are pure white, elongate, with an elaborate design in the sculp- 

 turing. The eggs of Blasturus cupidus (PI. LIV, Fig. 68) are 

 slightly flattened and tablet-like. Upon these flattened areas 

 are irregularly scattered pits and bosses which appear shining 

 white in the glycerine and about the longitudinal circumference 

 is a shelf-like extension which bears a large number of strap- 

 shaped pegs. The eggs of Polymitarcys albus (PI. LIV, Fig. 69) 

 are roundly ovate and white. The body of the egg is nearly 

 smooth, but the prominent yellow micropylar apparatus has 

 a distinctly shingle-like surface. The eggs of Callibagtis 

 fluctuans and Chirotonetes albomanicatus were perfectly 

 smooth and pure white. 



Nymphs of Hexagenia variabilis and Polymitarcys albus 

 live in the same situations but the eggs of the former are only 

 a little roughened, while Polymitarcys has the prominent 

 micropylar apparatus just described. The roughness due 

 to chorionic sculptures may be of some slight service in helping 

 to lodge the eggs, but its significance is probably slight. The 

 extensions of the chorion, on the other hand, are no doubt of 

 much importance in the dispersal and safety of the eggs. The 

 anchors upon Ephemerella rotunda and Tricorythus allectus 

 hang the eggs upon sticks and stems and prevent them from 

 being buried in the mud; the many viscid threads upon those 

 of Leptophlebia and Ecdyurus maculipennis accomplish the 

 same result in a different fashion. Those which probably 

 have the most important function are the long threads upon 

 the eggs of Heptagenia interpunctata. A number of these 

 were shaken about in water strewn with chara and the threads 

 immediately became closely entangled upon its stems. Eggs 

 thus hung upon stems in natural conditions would be safe- 

 guarded and prevented from being buried in the mud. 



Ameletus ludens 



Blasturus cupidus 



Callibaetis fluctuans 



Chirotonetes albomanicatus 



Choroterpes basalis 



Ecdyurus maculipennis 



Ephemerella excrucians 



Tricorythus allectus 



Number of 



egg in both 



ovaries 



670 

 3700 



500 

 2500 



1000 



1950 



750 



Color of 



Length 



(Fresh e 



'tired in gl 



Light brown' 



White 



White j 

 Pale green ! 



White i 



White 



White 



Green j 



.276 mm. 

 .177 mm. 



.200 mm. 

 .174 mm. 

 .170 mm. 

 .200 mm. 

 .189 mm. 



Width 

 ggs meas- 

 ycerin) 



.153 mm. 

 .093 mm. 



.138 mm. 

 .085 mm. 

 .133 mm. 

 .125 mm. 

 .122 mm. 



