84 THE ENTOMOLOGIST. 



that the series of affinities in nature is a concatenation or 

 continuous series; and that though an hiatus is here and 

 there observable, this has been caused either by the annihi- 

 lation of some original group or species or that the 



objects required to fill it up are still in existence, but have 

 not yet been discovered." Modern naturalists find in this 

 more or less gradual blending their strongest argument in 

 favour of comnninity of descent; and speculation as to the 

 origin, or outcome rather, in the near present or remote past, 

 of existing forms, is naturally and very generally indulged, 

 even by those who a few years back were more inclined to 

 ridicule than accept Darwinian doctrine. Shall we then say 

 that the old divisions must be discarded because not abso- 

 lute ? As well might we argue for the abolition of the four 

 seasons because they differ with the latitude, or because they 

 gradually blend into each other. Entomologists will always 

 speak of moths and butterflies, howsoever arbitrary the groups 

 may come to be looked upon, or however numerous the 

 intermediate gradations. These thoughts naturally present 

 themselves in considering so osculant a species as the Yucca 

 borer. 



The entomological reader is aware that the queenly 

 Yuccas cradle and nourish a very curious and anomalous 

 Lepidopteron — the Pronuba yuccasella. The genus is further 

 interesting, from the entomological side, as giving us the 

 insect under consideration. Jn the home of the Yuccas, and 

 more particularly in the home of the caulescent species, like 

 Y. aloifolia and Y''. gloriosa, persons who have occasion to dig 

 up the roots, or subterranean trunks, often notice that these 

 are bored and hollowed out along the axis, the burrow 

 cylindrical, and lined at its upper end with silk, which is 

 generall}' intermixed with a white, glistening, soapy powder. 

 These tunnellings are made by our Yucca borer, which 

 dwells therein ; and their presence may generally be detected 

 by masses of excrement observable amongst the leaves, and 

 by certain chimney -like projections made by the twisting and 

 webbing together of the more tender heart-leaves, or even of 

 the flower-stalk, after they have been partly devoured, into a 

 sort of funnel, from which the excrement is expelled. The 

 tunnellings weaken the trunk and induce rot, so that the 

 plant is not unfrequently ])rostrated thereby ; and as the 



