376 'Annals Entomological Society of America [Vol. VI, 



Fritze, 1889. Fritze, '89, studied the structure of the 

 alimentary canal. He described and figured a muscular 

 apparatus in the oesophagus, and discussed its changes of 

 function in the adult. 



Heymons, 1896. In a paper upon the embryology of Ephe- 

 mera vulgata, Heymons, '96, stated that the eggs hatched 

 eleven days after they were laid. He traced the development 

 of the nymphs up to the age of four days. He discussed the 

 ancestry of May-flies, and concluded that their life was ori- 

 ginally entirely aerial and that the closed tracheal system of 

 the nymphs is an accomodation to aquatic life. 



Causard, 1896. Causard noted the birth of living young 

 in Ephemera vivipare and briefly described the development 

 of the nyrnphs. 



Hubner, 1902. Hubner, '02, tested the regenerative powers 

 of nymphs of Cloeon dipterum. Certain nymphs regenerated 

 the last abdominal segment with its appendages. The ali- 

 mentary canal became functional, and the insect lived for 

 one month. 



Tumpel, Needham and Betten, 1901. In the same year 

 two general papers were published. "Die Geradflugler Mittel- 

 europas" by Tumpel and several complete life histories in 

 "Aquatic Insects of the Adirondacks" by Needham and 

 Betten. 



A similar but much more extensive work by Needham 

 followed in 1905 and 1908. In the introduction to this study 

 May-fly nymphs were described as "perhaps the dominant 

 insect herbivores of fresh water." Their herbivorous diet 

 and their importance in the economy of aquatic life were for 

 the first time emphasized. 



Sternfeld, '07. Sternfeld, '07, worked upon the atrophy of 

 the mouth-parts and the changes in function of the alimentary 

 canal. He reviewed Fritze's paper and considered the bio- 

 logical significance of the structures much more fully. He 

 concluded that the alimentary canal in imago May-flies is 

 by no means rudimentary and that a muscular apparatus, 

 which is under voluntary control, regulates the supply of air 

 in it. The decrease of specific gravity caused by this "swim- 

 ming bladder" aids the insects in the mating flight and hence 

 indirectly influences their multiplication. 



