HISTORICAL. 



drop of fluid that exuded was touched to a glass slide and the smears made in 

 the usual manner. They were fixed in absolute alcohol for 15 minutes. This 

 has the added advantage of dissolving the fat. Smears were stained with Giemsa's 

 blood stain (1 drop: 1 cc. distilled HoO) for 20 minutes, and rinsed in distilled 

 water until the better-spread portions had a pinkish tint. Smears were also 

 fixed in Helly's fluid and used as checks on the ordinary smears. 



Ill— HISTORICAL 



The earliest work on the embryology of May-fly mouth-parts is probably 

 that published by Burmeister in 1848. He mentions the rudiments of the mouth- 

 parts in Palingenia horaria twelve days after oviposition. N. Joly in 1876 wrote 

 a paper on the embryology of Palingenia virgo. He figures the mouth-parts 

 during the later stages of development, and says that they are modified con- 

 siderably before they reach their ultimate form. Heymons, 1896, gives general 

 figures of the mouth-parts of Ephemera vulgata. He erroneously calls the 

 mandibular tusk the "morphological equivalent of a mandibular palp." 



The greater part of the work on the mouth-parts of May-fly nymphs has 

 been published by systematists. Among the earlier workers. Pictet 1843, Hagen 

 1849-90, and Eaton 1883-6, stand pre-eminent. Needham 1901-8 published a 

 kev for the separation of our common North American genera of May-fly nymphs, 

 and grouped them in three sub-families. A large number of nymphs were also 

 described from bred specimens. His life-history work was followed by that of 

 Morgan 1911, and Clemens 1913-17. Morgan 1913 gives a very complete bibli- 

 ography and historical review of the entire field. She treats the modifications 

 of the mouth-parts as an adaptation to environment. The main lines of specializa- 

 tion in the three sub-families are sketched, and the details of the mouth-parts. 

 There is a discussion of food, and the function of the individual mouth-parts in 

 feeding. 



The atrophy of May-fly mouth-parts during aerial life has long been a 

 matter of observation among students of this group. In 1661 Johann Swammer- 

 dam writes: "In the adult condition these insects (Ephemeridae) do not eat, as 

 is the case with various other insects. The mouth-parts and alimentary canal of 

 the winged fly are completely useless and empty." Wolter, 1883, speaks of the 

 fusion of the labial segments in the imago. In 1907 Sternfeld says that degenera- 

 tion begins in the late nymph. Loss of segmentation is the main difference in 

 the mouth-parts of subimago and imago. He concludes that the form of the 

 mouth-parts is highly variable among the different genera. 



