THE YUCCA MOTE AND YUCCA POLLINATION. 179 



spines on the back, which are well fitted to enable it to work its 

 way to the surface from its underground retreat. 



The effect of the puncture of the female moth in oviposition is 

 at once noticeable on the young fruit by a darker green discolora- 

 tion externally. In time this becomes a depression, and the irregu- 

 larities of the pods (Fig. 9, d, e ; Fig. 10, 6, c) which have been con- 

 sidered characteristic of the fruit of the genus are chiefly due to 

 these punctures, which, ordinarily occurring just below the mid- 

 dle of the pod, produce a more or less marked constriction there. 



Vii 



*l 



Fig. 9. a, longitudinal section of pistil of Yucca Jilamentosa, showing (5, b) punctures of Pro- 

 nuba, and (c, c) the normal position of her eggs in the ovarian cell ; d, section of a punct- 

 ured carpel seven days after oviposition, showing the egg yet unhatched and the manner 

 in which the ovules in the neighborhood of puncture have been arrested in development 

 so as to cause the constriction ; e, section of an older carpel, showing the larva above the 

 original puncture ; /, a seed thirteen days from oviposition, showing young larva at funic- 

 ular base. 



This I have often proved by artificially pollinizing the flowers 

 and protecting them from Pronuba, when the pods will develop 

 in a regular, parallel-sided manner (Fig. 10, a). 



It is noticeable that all the pods do not contain Pronuba 

 larva3, though we rarely find any on the filamentose species that 

 do not show the marks of puncture, which indicates that a great 

 many punctures are fruitless in result, owing either to the diffi- 

 culty of the operation of oviposition, or to the fact that the eggs, 

 having been once consigned to the pistil, have failed to hatch, for 

 one reason or another ; or again, that the larva has, for one reason 

 or another, perished. A similar mortality is connected with the 



