DISPERSION OF POLLEN BY ANIMALS. 159 



pollen into the stigma in order that its grubs may be supplied with the nutriment 

 requisite for the preservation of the species — nutriment which would not be 

 forthcoming unless the ovules were fertilized. 



This inference does not, of course, involve the assumption that the operations 

 in question are carried out deliberately by the moth with an intelligent foresight 

 of the results. But there is no objection to our looking upon the habits of these 

 insects as unconsciously purposeful. The stuffing of the pollen into the stigmatic 

 funnels is neither more nor less wonderful than the fact that in remote valleys 

 where the population is very sparse and there are very few vegetable gardens, the 

 cabbage white butterfly often flies miles away to look for cabbages upon which it 

 may lay its eggs so that the grubs may find the food that suits them the moment 

 they are hatched. Equally marvellous, too, is the case of many kinds of caterpillar 

 which spin their cocoons on the bark of trees, and cover the structures wherein 

 they are subsequently to undergo transformation into the chrysalis-state with 

 lichens and fragments of bark, that their temporary resting-place may not be 

 noticed by insectivorous birds; and again the same sort of phenomenon encounters 

 us in the case of the caterpillars which live in the interior of the hard parts of 

 plants, and before transforming themselves into pupae make a special exit ready for 

 the soft and delicate imago subsequently to be liberated. 



It must be observed that the grubs of Pronuba yuccasella do not eat up all 

 the developing seeds of the ovary in which the moth lays her eggs. There are 

 about 200 ovules in each ovary. Even if half or two-thirds of them are consumed, 

 there is still a sufficient number of uninjured seeds left to be scattered abroad when 

 they have reached maturity, whereas without the intervention of the moth not 

 a single seed capable of germination would have been produced. Whether or not 

 symbiosis with moths also occurs in the species of Yucca bearing berries has not 

 been ascertained for certain; but seeing that the berry-producing species, Yucca 

 aloefolia, Y. Treculeana, &c., have been found to have holes in all their mature 

 fruits — at least when they are growing in their native countries (Florida, Carolina, 

 Mexico, Louisiana, Texas) — and other traces have been discovered pointing to their 

 having been occupied by caterpillars, the probability is very strong that such is the 

 fact. 



Still more remarkable than the relation between the genus Yucca and its 

 companion moth is that existing between Fig-trees and certain small wasps of 

 the group of the Chalcididee. To understand the relation clearly, it is first of all 

 necessary to examine the construction of the inflorescence in the Fig. Looking 

 at a fig that has been cut open lengthwise, as is shown in fig. 240 ^, it is observed 

 that it is not a simple flower, but rather a whole collection of flowers inclosed 

 in an urn or pear-shaped receptacle. These pear-shaped shoots are in reality 

 hollow inflorescences bearing numerous flowers on their inner walls. Each fig is 

 termed a synconium. The orifice of the urn is very small, and is further straitened 

 by the presence of small leafy scales. The flowers, which are very simple in 

 structure, almost fill the entire cavity; they are of two kinds, male and female. 



