310 



channels, the substance of the stem being less firm tlian that of the 

 other species of Yucca. In so far, therefore, as this particuhir I'ro 

 doxus larva has peculiar structures we can trace their origin to purely 

 dynamic influences, assisted by heredity and selection — a consequence, 

 in other Avords, of environment — and repeated independently in larvae 

 of difterent orders having no possible genetic connection. 



The distribution of the genus Pronuba as exemplified in these addi- 

 tional observations is extremely interesting. Pronuba yuccasella, the 

 typical species of the genus, not only occurs over half the continent, as 

 I have previously shown, but extends to the Pacific coast, and is found 

 as far south as San Diego, showing over this wide range absolutely 

 no difterences that would justify varietal designation. All the charac- 

 ters are absolutely the same, and the rather dark coloring of the horny 

 and chitinous parts of the body in the California, Dakota, and Colo- 

 rado specimens would indicate that the western forms have this pecu- 

 liarity as compared with the eastern. This species is now known to 

 pollinize all the true Yuccas so far studied, and accompanies them 

 across the continent. It thus pollinizes Yucca Jilamcntosa and its sev- 

 eral forms in the northeast ; Y. yloriosa, and Y. aloifolia in the south- 

 east; Y. angiisfifolia {glauca) in the Rocky Mountain regions; Y. rupi- 

 cola and Y. data in the southwest; and Y. haccata, which connects the 

 territory of Y. aiigtisti/oJi'a with that of Y. hrcvifolia and Y. a-hipplcL It 

 thus occurs in the same territory as its two congeners, Fronuba si/n- 

 thetica and P. niaculata, with its atcrrima variety, while these last are 

 restricted to their respective Yuccas. This fact, as Prof. Trelease has 

 pointed out, strengthens the inference that brcvifolia and ichipjjlei are 

 primary Pacific coast types, while baccata is an immigrant from the 

 east. It remains yet to observe the ])ollinizers associated with Yucca 

 JiUfera, Y. austraUs, Y. treculeana, and Y. (juaiemalcnmH, each of which 

 will probably have a distinct Pronuba, while the other Yuccas not 

 enumerated here will probably not have distinct species connected 

 with them. 



It would carry ine too far to speculate further on the additional facts 

 brought forth, but I would urge in conclusion that in all ^Ir. Trelease's 

 interesting observations in his special studies of these different species 

 of Yucca, and after having paid particular attention to the point, he has 

 failed to see a single Pronuba in any species attempt to feed on either 

 the stigmatic secretion or the septal nectar. He was also unable to 

 convince himself that in any case the insect makes use of the tongue 

 in pollination, as he once thought it might. In this and other respects 

 he fully confirms the conclusions which I have drawn in my previous 

 communication to the Society, while the additional data which I have 

 indicated give further force to my remarks upon variation, as exemplified 

 by these Prodoxids. 



