A CONTRIBUTION TO THE BIOLOGY OF MAY-FLIES,* 



Anna H. Morgan. 



CONTENTS. 



I. Introduction 371 



II. Historical 372 



III. Life Cycle 377 



Embryo, Nymph, Sub-imago, Imago. 



IV. Modifications of structures of the nymph 380> 



Habitat, Shape of body. Gills, Food, Mouth-parts, Legs. 



V. Modifications of Adult Structures '. . . . 392: 



Mating, Alimentary Canal, Legs, Genitalia. 



VI. Eggs 397 



VII. Bibliography of the Order 401 



I. INTRODUCTION. 



This is a study of the habits and structure of May-flies. 

 It describes the situations in which they Hve and some of the 

 adjustments which they have made to the conditions in them. 

 The two problems which face every organism are those of 

 maintaining its own life and continuing its race. Its youth is 

 devoted entirely to satisfying its individual needs for food and 

 safety; its adult life is devoted to the race, but the necessities 

 of the individual are still satisfied though they may be secured 

 in an entirely different way. The immature life of May-flies 

 is aquatic, and to it all adjustments concerned with food 

 or safety are exclusively confined. The mature or adult life 

 is aerial. It is solely devoted to reproduction. There is no 

 provision for food or for other means of lengthening its 

 life. It gives an opportunity for studying ways of getting 

 a living which have been completely isolated from ways of 

 reproducing. The study which follows has been divided 

 into five sections. 



1. The historical sketch, in which the more important 

 papers which have dealt with May-fly biology are briefly 

 discussed. 



2. The life cycle which consists of a brief statement 

 of the characteristics of the three stages of life. 



3. The evolution of the nymphs in which progress from a 

 generalized to a specialized condition is shown in changes of 

 shape and function of gills, mouthparts, and legs. 



*Contribution from the Limnological Laboratory of Cornell University. 

 This work was done under the direction of Professor James G. Needham, of whose 

 kindly criticism and stimulating interest I wish to express my appreciation. I 

 wish also to thank Miss Anna C. Stryke for her many helpful suggestions regarding 

 the drawings and the photographs from which some of the drawings have been 

 taken. 



371 



