x AUTHOR’S PREFACE 
Some of these works, for instance those of Alfken, Dalla Torre, Frey, 
Friese, Hoffer, Krieger, Morawitz, Schletterer, and Sickmann, contain in 
places an amazing amount of material for use by the flower specialist, 
and frequently afford the only available information as to visitors to 
flowers. Others, on the contrary, as, for instance, André’s work, which 
is in many volumes, contain only a few useful notices. There are numerous 
other entomological works, especially in French and Italian, which might 
have been referred to, but to have done so would have greatly increased 
the toil of compilation; and it is questionable if the result would have 
repaid the labour. Some, indeed, of the works that were looked into 
contained no useful information at all, as, for instance, Aurivillius (Gronlands 
insektfauna ; Vet.-Ak. Bih., Stockholm, Vol. xv, Ser. 4, Nr. 1, pp. 1-33) 
and F. Chevrier (Description des Chrysides du Bassin du-Léman, Geneva, 
1862) 1. 
Herr D. Alfken has placed at my disposal his valuable observations 
on the visits of insects to flowers in the neighbourhood of Bremen. Some 
observations of Hans Hoppner, that also refer to the neighbourhood of 
Bremen, are added. Further, Herr Alfken has communicated to me, in 
addition to his previously published observations on the Island of Juist, 
a number of new ones. 
Besides my own observations on the visits of insects to flowers, and 
in addition to those of Borgstette, Buddeberg, Burkill, Cobelli, Darwin, 
Delpino, Ekstam, Heinsius, Lindman, Loew, MacLeod. Hermann Miller, 
Plateau, Rathay, Ricca, Schneider, A. Schulz, Scott-Elliot, Sprengel, 
Verhoeff, de Vries, Willis, and Wittrock, there is a very considerable mass 
of work containing material useful in studying flower pollination ; 
so that here again only a relative independence can be claimed. The 
‘tedious’ lists of visitors, in which thousands of individual observations 
are set down, form the indispensably necessary statistical material upon 
which to base our knowledge of the relations subsisting between groups 
of flowers and insects. They afford an insight into the connection between 
the structure of flowers and the anatomical characters of insects ; they tell 
us that everywhere flowers are sought out in preponderating majority by 
such insects as are modified in adaptation to them. I reserve this statistical 
material for working up afresh. 
It must be admitted that in the enumeration of visitors, the record 
1 There were also no observations on flower pollination in works that I looked through by 
M. J. Pérez (Contributions 4 la faune des Apiaires de France, II* partie, Parasites. — Actes soc. 
linn, Bordeaux, 1883) and by Ruggero Cobelli (Gli imenotteri di Trentino, Fasc. I: Formicidae, 
Rovereto, 1887; Fasc. II: Tenthredinidae, Apidae, Chrysididae, Pompilidae, Scoliadae, Mutillidae, 
Sapygidae, 1891; Fasc. III: Vespidae. — Sphegidae, 1893; Fasc. IV: Evanidae, Cynipidae, Chal- 
cididae, Proctotrupidae, Ichneumonidae, Braconidae, 1897). 
