INSECTS AND FLOWERS 237 



its allies. When bent on egg-laying, the females have 

 frequently been observed to carry pollen from the anthers 

 of one bloom to the stigma of another ; and but for this 

 exchange the plants might be infertile. The reader will 

 perceive, however, that the device is not above criticism, 

 seeing that the young caterpillars are destined to destroy 

 the very seed which their parent has helped to produce. 

 In practice, however, the seeds in a given capsule are 

 seldom all destroyed, while the same plant always bears 

 uninjured capsules which owe their fertility to the visits 

 of male moths, or of females which have exhausted their 

 store of eggs. 



The relations which exist between the American 

 yuccas and certain small, white-winged moths of the 

 genus Pronuba are even more extraordinary. The facts 

 were first ascertained by Professor C. V. Riley, whose 

 detailed account of the fertilisation of Yucca Ji lam entosa 

 by Pronuba yuccasella is here summarised. The male 

 moth is not specially remarkable, but the female is fitted 

 for her peculiar duties by modifications which are unique 

 among scale-winged insects. Not only are her maxillary 

 palpi well developed (the reader will remember that in all 

 other moths these organs are either very small or altogether 

 wanting), but she carries in addition a pair of long, pre- 

 hensile " tentacles " which are without precedent among 

 her kith and kin. She is also equipped with a long pro- 

 trusible ovipositor which combines in itself the functions 

 of a lance and a saw. She makes her debut simultaneously 

 with the blooming of the yucca, and frequents the flowers 

 soon after dark. So intent is she upon her duties that she 

 will continue to work even in the light of a lantern. 

 Clinging to a stamen, she first scrapes off the pollen with 

 her abnormal tentacles. She then raises her head, and 

 commences to shape the precious grains into a little 



