310 



cliannels, the substance of the stem being less firm than that of the 

 other species of Yucca. In -so far, therefore, as this i)articular Pro- 

 doxus larva has i^eculiar structures we can trace their origin to purely 

 dynamic inHuences. assisted by heredity and selection — a consequence, 

 in other words, of environment — and repeated independently in larvie 

 of different orders having no possible genetic connection. 



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

 tional observations is extremely interesting. Froniiha yuccaseUa, 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 differences that would justify varietal designation. All the chara-c- 

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

 and chitiiious 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 

 13ollinize all the true Yuccas so far studied, and accompanies them 

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

 eral forms in the northeast: Y. gloriosa and Y. a?o?yb/m in the south- 

 east: Y. august if olia iglauca) in the Eocky Mountain regions; Y. rujyi- 

 coJa and Y. elata in the southwest; and Y. haccata, which connects the 

 territory of Y. august ifoJia with that of Y. hrevifolia and Y. wliippleL It 

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

 tlietica and P. inaculata. with its aterrima variety, while these last are 

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

 pointed out. strengthens the inference that hrevifolia and ichipplei are 

 primary Pacific coast ty[3es, while haccata is an immigrant from the 

 east. It remains yet to observe the pollinizers associated with Yucca 

 filifera. Y. acstralis. Y. frecuJeaua. and Y. g/'ateu/aJetisis. e-dcli of ^^hich 

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

 enumerated here wiU probably not have distinct species connected 

 with them. 



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

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

 interesting observations in his special studies of these different si^ecies 

 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 i)ollination. as he ouce thought it might. In this and other respects 

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

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

 indicated give farther force to my remarks upon variation, as exemphfied 

 bv these Prodoxids. 



