374 Annals Entomological Society of America [Vol. VI^ 



in the setae the two currents of blood which have since been 

 carefully studied. 



Westwood, 1840. In 1840 Westwood discussed the classi- 

 fication of May-flies, following the discussion with some bio- 

 logical facts mostly gathered from previous writers. 



Burmeister, 1848. Burmeister made the first real con- 

 tribution to May-fly embryology. . While sitting in his room 

 one evening, many females of Palingenia horaria flew through 

 the open window and began depositing eggs upon his table. 

 Burmeister described these eggs and figured them. He placed 

 some of them in water on July 22 and on August 2 he freed 

 an embryo from the shell. He studied this stage carefully 

 and figured it showing the mouth-parts, legs and gills. 



Leuckart, 1858. Ten years later Leuckart carefully de- 

 scribed the eggs of three May-flies. This work was f ^)llowed by 



Grenacher, 1868. Grenacher's short, but important paper, 

 "Beitrage zu Kenntniss des Eies der Ephemeriden." . He 

 studied eggs similar to those cited by Leuckart and showed that 

 the polar knobs described by him were to be found in various 

 stages within the ovary. So far as known, Leuckart and 

 Grenacher have been the only authors who have made any 

 careful study of these egg structures in May-flies. 



Pictet, 1843. The first general study of this group was 

 the monograph in the ''Historic Naturelles des Insectes Neu- 

 ropteres" by Pictet. He classified preceding biological and 

 systematic studies and gave a history of each, reviewing all 

 of the most important contributions from Aristotle to 1840. 

 He described the habits of his four classes of nymphs, fossorial, 

 flattened, swimming and crawling. He discussed the emergence 

 of the nymph and features of the sub-imago and imago stages, 

 but he gave many details less satisfactorily than Swammerdam 

 or Geoffroy. 



Dufoiir, 1849. In 1849 Leon Dufour published a memoire 

 on the different kinds of respiration in insects. In this he 

 classified May-flies with insects breathing by means of external 

 organs. This study was followed by the similar ones of Mueller, 

 1851, and Milne Edwards, 1857. 



Lubbock, 1863-6. After the first contribution to May- 

 fly embryology by Burmeister in 1848, no further investigations 

 were made until 1863-6, when Sir John Lubbock published 

 two papers, "On the Development of Chloeon dimidiatum." 



