OF NATURAL SELECTION. 173 



movements through irritability or elasticity. From such 

 structures we may advance till we come to such a case of 

 extraordinary adaptation as that lately described by Dr. 

 Criiger in the Coryanthes. This orchid has part of its 

 labellum or lower lip hollowed out into a great bucket, into 

 which drops of almost pure 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 purpose 

 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 ouuld not fly away, but were compelled to crawl 

 out through the passage formed by the spout or overflow. 

 Dr. Criiger saw a " continual procession " of bees thus crawl- 

 ing 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, £ rst 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 fertilized. Now, at last we see the full use of 

 every part of the flower, of the water-secreting horns of the 

 bucket half-full of water, which prevents the bees from flying 

 awa} T , and forces them to crawl out through the spout, and 

 rub against the properly placed viscid pollen-masses and the 

 viscid stigma. 



The construction of the flower in another closely allied 

 orchid, namely, the Catasetum, is widely different, though 

 serving the same end; an4 is equally curious, gees visit 



