202 



THE EVOLUTION THEORY 



contradictory to, but is corroborative of, the theory of selection. The 

 excellent American entomologist, Riley, established by means of 

 careful observations that the large white flowers of the Yucca are 

 fertilized by a little moth which behaves in a manner otherwise 

 unheard of among insects. Only the females visit the flowers, and 

 they at once busy themselves collecting a large ball of pollen. To 

 this end they have on the maxillary palps (Fig. 52, C, mxp) a long 

 process (si), curved in the form of a sickle, and covered with hairs, 

 which probably no other Lepidopteron possesses, with the help of 

 which the moth very quickly sweeps together a ball of pollen, it 

 may be three times the size of her own head. With this ball the 

 insect flies to the next flower, and there she lays her egg, by means of 



Fig. 52. The fertilization of the Yucca. A, ovipositor of the Yucca-moth. 

 op, its sheath, sp, its apex, op 1 , the protruded oviduct. B, two ovaries of the 

 Yucca, showing the holes by which the young moths escape, and (r) a 

 caterpillar in the interior. C, head of the female moth, with the sickle-shaped 

 process (si) on the maxillary palps for sweeping off the pollen and rolling it 

 into a ball. mx x , the proboscis, au, eye. p 1 , base of first leg. D, longitudinal 

 section through an ovary of the Yucca, soon after the laying of two eggs (ei). 

 stk, the canal made by the ovipositor. 



an ovipositor otherwise unknown among Lepidoptera (Fig. 52, A, op), 

 in the pods of the flower. Finally, she pushes the ball of pollen deep 

 into the funnel-shaped stigmatic opening on the pistil (Fig. 51, n), and 

 so effects the cross-fertilization. The ovules develop, and when the 

 caterpillars emerge from the egg four to five days later they feed on 

 these until they are ready to enter on the pupa stage. Each little 

 caterpillar requires about eighteen or twenty seeds for its nourishment 

 (Fig. 52, B, r). 



