128 ANIMAL INDIVIDUALITY [CH. 



mutual relation. Most flowers are fairly catholic in 

 their tastes, and are adapted for fertilization by a 

 number of different insects, and the same is true, 

 mutatis mutandis, of the insects. But sometimes 

 the relation is a much narrower one, till finally an 

 insect may be able to get food only from one particular 

 flower, the flower to be fertilized only by this parti- 

 cular insect. A relation of this degree of intimacy 

 (though with not quite the same purposes) is found 

 between the Yucca-plant and a moth of the genus 

 Pronuba (Fig. 13). Here (for the details I must again 

 refer the reader to other books ; e.g. (17), Vol. i, p. 201) 

 the Yucca can in nature only be fertilized by the one 

 agency of the moth : she, when the time comes for 

 egg-laying, flies to the Yucca, rakes up a large ball of 

 pollen by means of a unique structure on her head, 

 and then flies with the ball to another flower ; there 

 she sticks her long and curiously-shaped ovipositor 

 into the ovary of the flower, and lays her egg among 

 the unfertilized seeds inside. Last she lifts the pollen- 

 ball on to a special hollow on the top of the stigma, 

 and pokes it firmly down. The pollen fertilizes the 

 ovules, of which there are about two hundred, and 

 they start developing into seeds ; meanwhile the cater- 

 pillar hatches, and feeds at the expense of the seeds. 

 However, it only needs some twenty or so before 

 undergoing its transformations into pupa and moth, 

 and leaves the rest to grow into new Yucca-plants. 



