THE YUCCA MOTH AND YUCCA POLLINATION. 181 



those individuals of the larger, fleshy-fruited species like aloifolia 

 which happen to bloom about the same time of the year. 



Thus we find that some species of Pronuba is connected with 

 all the yuccas so far studied in this connection, and I have no 

 doubt that this will be found to be generally true, so far as the 

 indigenous species are concerned, and that in the native home of 

 any of the species we shall find that pollination depends upon 

 some species of Pronuba. This is rendered certain by the fact 

 that, wherever I have been able to examine the mature or partially 

 mature fruit of other yuccas in herbaria, I have in almost every 

 instance observed the constriction and in most instances seen 

 traces of the puncture and the work of the larva. 



We have, in the structures and functions which are so charac- 

 teristic of this yucca moth, admirable adaptations of means to an 

 end, whether for pollinizing the plant or providing for a future 

 generation. The Pronuba larva rarely destroys more than a dozen 

 of the seeds, so that several may develop within a single pod and 

 yet leave many perfect seeds, while, for the reasons already stated, 

 we occasionally have pods without a trace of the insect. 



There is between Pronuba and its food-plant a mutual inter- 

 dependence which excites our wonder, and is fraught with inter- 

 esting suggestions to those who are in the habit of reasoning 

 from effect to cause. Whether we believe, as I certainly do, that 

 this perfect adaptation and adjustment have been brought about 

 by slow degrees through the long course of ages, or whether we 

 believe that they were always so from the beginning, they are 

 equally suggestive. The peculiar structure of the flower which 

 prevents self-fertilization, though on a superficial view it strike 

 one as a disadvantage, is, in reality, of benefit, as the value of 

 cross-fertilization has been fully established ; while the maxillary 

 tentacles of the female moth are very plainly an advantage to her 

 species in the " struggle for life " ; and it is quite easy to conceive, 

 on Darwinian grounds, how both these characteristics have been 

 produced in the course of time from archetypal forms which pos- 

 sessed neither, and in reality we get a good insight into the pro- 

 cess in studying the characteristics of other species of the family 

 ProdoxidcB. These peculiarities are, moreover, mutually and re- 

 ciprocally beneficial, so that the plant and the animal are each in- 

 fluenced and modified by the other, and the same laws which pro- 

 duced the beneficial specialization of parts will maintain them by 

 the elimination of all tendencies to depart from them. 



The pollen grains would not adhere by chance to the rolled-up 

 tentacles, and we have seen how full of apparent purpose and de- 

 liberation Pronuba's actions are, It may be that all her actions 

 are the result merely of " blind instinct," by which term proud 

 man has been wont to designate the doings of inferior animals ; 



