60 PROBLEMS OF EVOLUTION 



able, of the feat performed, for instance, by the caterpillar of 

 the common silk moth when it spins its cocoon. 



The Yucca But this is nothing compared with what is done by a Cali- 

 fornian moth, Pronuba yuccasella, for a full account of which I 

 refer the reader to Kerner's Natural History of Plants. 1 The 

 caterpillar of this moth lives on the seed of the Yucca plant ; 

 this plant cannot fertilise itself, but must have pollen brought to 

 the stigma. The Yucca moth, armed with special appliances, 

 not only deposits its eggs where the caterpillars when they 

 emerge will have proper food, but accomplishes the transfer of 

 the pollen. At night when the yellowish white flowers are 

 open and visible in the moonlight, she starts forth on the 

 important business on which depends the continuance of her race. 

 She enters the bell of a flower and collects a ball of pollen. 

 For this purpose she makes use of the elongated first joint of 

 the maxillary palp, " the inner surface of which is beset with 

 stiff bristles and can be rolled up like a trunk." With this she 

 seizes the pollen, rolls it into a ball which is sometimes three 

 times as large as her head. She then flies to another flower and 

 proceeds to deposit her eggs at the base (which in a hanging 

 flower is uppermost) of the pistil. This she does by means of 

 an ovipositor consisting of four horny bristles which are able to 

 pierce the hard tissue. Having laid her eggs she goes to the 

 top of the funnel-shaped pistil and stuffs the pollen into the 

 mouth of the funnel. 



I will now draw attention to the various points that strike one 

 as one reads this remarkable story : (l) The adaptation of the 

 maxillary palp and the ovipositor ; (2) the correct use of the 

 special apparatus ; (3) the fact that the individual moth gains 

 nothing by the whole business ; (4) that each moth has only 

 once in its lifetime to do this work ; (5) The circumstances 

 seem to make it impossible that there can be any imitation, any 

 learning on the part of one individual from another. In the 

 presence of such facts what becomes of the Lamarckian hypo- 

 thesis ? 



One other point I must mention though it does not bear on 

 1 Vol. ii. p. 156. 



