II.] INCIPIENT STRUCTURES. 63 



but in his "Origin of Species" 1 he describes two which 

 must not be passed over. In one (Coryanthes) the orchid 

 has its lower lip enlarged into a bucket, above which 

 stand two water- secreting horns. These latter replenish 

 the bucket, from which, when half-filled, the water over- 

 flows by a spout on one side. Bees visiting the flower 

 fall into the bucket and crawl out at the spout. By the 

 peculiar arrangement of the parts of the flower, the first 

 bee which does so carries away the pollen-mass glued to 

 his back, and then when he has his next involuntary bath 

 in another flower, as he crawls out the pollen-mass attached 

 to him, comes in contact with the stigma of that second 

 flower and fertilizes it. In the other example (Catasetum), 

 when a bee gnaws a certain part of the flower, he inevitably 

 touches a long delicate projection, which Mr. Darwin calls 

 the antenna. " This antenna transmits a vibration to a 

 membrane, which is instantly ruptured ; this sets free a 

 spring by which the pollen-mass is shot forth like an 

 arrow in the right direction, and adheres by its viscid 

 extremity to the back of the bee ! " 



Another difficulty, and one of some importance, is pre- 

 sented by those communities of ants which have not only 

 a population of sterile females, or workers, but two distinct 

 and very different castes of such. Mr. Darwin believes 

 that he has got over this difficulty by having found indi- 

 viduals intermediate in form and structure 2 between the 

 two working castes ; others, may think that we have in this 



1 Fifth Edition, p. 236. 



2 Mr. Smith, of the Entomological department of the British Museum, 

 has kindly informed the author that the individuals intermediate in 

 structure are very few in number not more than five per cent. com- 

 pared with the number of distinctly differentiated individuals. Besides, 

 in the Brazilian kinds the^e intermediate forms are wanting. 



