268 THE ORIGIN OF SPECIES 



water continually fall from two secreting horns which 

 stand above it; and when the bucket is half full, the 

 water overflows by a spout on one side. The basal part 

 of the labellum stands over the bucket, and is itself 

 hollowed out into a sort of chamber with two lateral 

 entrances; within this chamber there are curious fleshy 

 ridges. The most ingenious man, if he had not witnessed 

 what takes place, could never have imagined what pur- 

 pose all these parts serve. But Dr. Criiger saw crowds 

 of large humble-bees visiting the gigantic flowers of this 

 orchid, not in order to suck nectar, but to gnaw off the 

 ridges within the chamber above the bucket; in doing 

 this they frequently pushed each other into the bucket, 

 and their wings being thus wetted they could not fly 

 away, but were compelled to crawl out through the pas- 

 sage formed by the spout or overflow. Dr. Criiger saw a 

 "continual procession" of bees thus crawling out of their 

 involuntary bath. The passage is narrow, and is roofed 

 over by the column, so that a bee, in forcing its way 

 out, first rubs its back against the viscid stigma and 

 then against the viscid glands of the pollen-masses. The 

 pollen-masses are thus glued to the back of the bee 

 which first happens to crawl out through the passage 

 of a lately expanded flower, and are thus carried away. 

 Dr. Criiger sent me a flower in spirits of wine, with a 

 bee which he had killed before it had quite crawled out 

 with a pollen-mass still fastened to its back. When the 

 bee, thus provided, flies to another flower or to the same 

 flower a second time, and is pushed by its comrades 

 into the bucket and then crawls out by the passage, 

 the pollen-mass necessarily comes first into contact with 

 the viscid stigma, and adheres to it, and the flower is 



