THE OEIGIN OF FliOWEKS 193 



mentioned, Prosopis, takes up pollen and nectar in its mouth, and 

 afterwards disgorges the pulp as food for its larvae, but the rest of 

 the true bees have special and much more effective collecting-organs, 

 either a thick covering of hair on the abdomen, or along the whole 

 length of the posterior legs, or finally, a highly developed collecting 

 apparatus, such as that possessed by the honey-bee — the basket and 

 brush on the hind leg. The former is a hollow on the outer surface 

 of the tibia, the latter a considerable enlargement of the basal tarsal 

 joint, which, at the same time, is covered on the inner surface with 

 short bristles, arranged in transverse rows like a brush. The bee 

 kneads the pollen into the basket, and one can often see bees flying 

 back to the hive with a thick yellow ball of pollen on the hind leg. 

 In those bees which collect on the abdomen, like Osmia and Megachile, 

 the pollen mass forms a thick clump on the belly, and in the case 

 of Andrena Sprengel observed long ago that it sometimes flew with 

 a packet of pollen bigger than its own body on the hind leg. 



All these are contrivances which have gradually originated 

 through the habit of carrying home pollen for the helpless larvae shut 

 up in the cells. They have developed differently in the various 

 groups of bees, probably because the primary variations with which 

 the process of selection began were different in the various ancestral 

 forms. 



In the ancestors of those which carry pollen on the abdomen 

 there was probably a thick covering of hair on the ventral surface of 

 the body, which served as a starting-point for the selection, and, 

 in consequence, the further course of the adaptation would be con- 

 cerned solely with this hair-covered surface, while variations in other 

 less hairy spots would remain un-utilized. 



After all this it will no longer seem a paradoxical statement that 

 the existence of gaily coloured, diversely formed, and fragrant flowers 

 is due to the visits of insects, and that, on the other hand, many 

 insects have undergone essential transformations in their mouth-parts 

 and otherwise as an adaptation to a flower diet, and that an entire 

 order of insects with thousands of species— the Lepidoptera — would 

 not be in existence at all if there had been no flowers. We must now 

 attempt to show, in a more detailed way, how, by what steps, and 

 under what conditions, our modern flowers have arisen from the 

 earlier flowering plants. In this I follow closely the classic exposition 

 which we owe to Hermann Miiller. 



The ancestral forms of the modern higher plants, the so-called 

 ' primitive seed plants ' or ' Archisperms,' were all anemophilous, as 

 the Conifers and Cycads are still. Their smooth pollen-grains, 



