PART Iv. | GENERAL RETROSPECT. : 579 
flowers, that it became possible for long-proboscised varieties of 
entomophilous insects to vanquish their short-lipped relatives in 
the struggle for existence. This tendency of natural selection 
must have taken effect the more certainly, in each class of insects, 
the more the insects were dependent on a floral diet. 
To give a clear view of the effect of simple concealment of the honey in 
flowers with exposed anthers, I have tabulated the visitors of certain groups of 
flowers in which the honey is fully exposed, others in which it is more deeply 
situated but still visible, and others again, in which it is quite concealed. The 
following is a summary of the result :— 
(a) On the twenty-five Umbellifere treated in detail in Part III., whose 
flowers contain honey freely exposed in a smooth, adherent layer, I have 
observed 757 distinct insect-visits ; that is to say, an average of 30 to each 
species. 
(6) On thirty-eight species of flowers whose honey is still visible, but is 
placed more or less deeply at the base of a regular flower, and accumulates in 
somewhat greater quantity (Crucifere, Nos. 27—41; Polygonum, Nos. 369— 
374; Alsinea, Nos. 60—67; Rosacew, Nos. 128, 133, 135, 150--153), I 
have observed 582 distinct insect-visits, or on an average 15 to 16 to each 
species. 
(c) On twenty-seven species of flowers whose honey is not directly visible 
but is yet accessible to the most short-lipped insects (Geraniacew, Nos. 76—83 ; 
(Malva, Nos. 69—72; Epilobium, No. 166; Campanula, Nos. 277—282 ; 
Jasione, No, 283; Ranunculus, Nos. 6—10) I have observed 384 distinct 
insect-visits, or an average of 13 to 14 to each species. 
If we classify these visits according to the classes to which the insects belong, 
and subdivide these classes, when necessary, according to the lengths of the 
insects’ proboscides, we find the following number per thousand visits, for each 
of the above-mentioned group of flowers :— 
(1) Orthoptera, Neuroptera, and Hemiptera: (a) 12; (b) 3; (ec) 3. 
(2) Coleoptera: (a) 84; (b) 168; (c) 76. 
(3) Long-tongued Diptera: (a) 84; (b) 167 ; (ec) 78. 
Bombylius, Empis, and Conopide: (a) 15; (b) 40; (c) 26. 
Eristalis, Helophilus, and Volucella: (a) 69; (b) 105; (c) 36. 
Rhingia: (a) 0; (6) 22; (c) 16. 
(4) Short-tongued Diptera: (a) 289 ; (b) 250; (c) 180. 
(5) Apide: (a) 127; (b) 292; (c) 524. 
Prosopis : (a) 25; (b) 143 (ce) 42. 
Sphecodes, Andrena, and Halictus : (a) 86; (b) 175; (ce) 250. 
Other bees with moderately long tongues: (a) 15; (b) 70; (ec) 180. 
Bombus and Anthophora: (a) 1; (0) 33; (c) 52. 
(6) Other Hymenoptera : (a) 332; (b) 69; (c) 91. 
(7) Lepidoptera: (a) 8; (b) 41; (e) 44. 
(8) Thrips: (a) 0; (b) 10; (ce) 5. 
However imperfect my lists may be, and however small the value that we 
can give to particular numbers, this table shows clearly that with increased 
PP 2 
