370 
Yucca brevifolia is pollinized by Pronuba synthetica Riley, the most 
remarkable species of the genus, having very stout maxillary tentacles, 
a very Stout ovipositor, shorter than that of yuccasella, but character- 
ized chiefly by having fuliginous and unscaled wings, and a polished, 
naked, and flattened body—structures all well adapted for crawling 
between and about the compact and crowded flowers, with their thick 
and leathery petals, but very abnormal in the Lepidoptera. In fact, 
this species strongly recalls in its general aspect some of the saw-flies 
belonging to the genus Dolerus, the resemblance being heightened by 
the rather conspicuous, cenchri-like spots, and by the conspicuous divi- 
sion between the thorax and abdomen. It also strikingly recalls some 
of the Neuroptera, as Sialis infumata. 
Now, these resemblances to insects of different Orders, and to families 
which are generally considered to be of low type within their Order, 
can not possibly be mimetic, as there can be no conceivable cause, pur- 
pose, or advantage in the mimicry. It is also impossible to account 
for these resemblances upon any present genetic connection. Yet we 
are hardly justified in disposing of them as merely accidental and with- 
out meaning. They suggest a possible synthesism in the past, when 
types were less specialized and present Orders had not become so well 
differentiated. 
Yueca whipplec, which occurs in southern California, has flowers dis- 
tinguished by their relatively long and stout stamens, the pollen of 
which is copious and glutinous, not to say mucilaginous, and a short, 
contracted style, with the stigma, however, expanded and covered with 
sticky threads. Itis pollinized by Pronuba maculuta Riley, which, as 
already shown, has a tongue modified into an accessory pollen-gathering 
organ. Ifany species of Yucca would seem not to need a special in- 
sect for pollination, Yucca whippleiis that species; for the long stamens, 
the sticky and abundant pollen, and the peltate, hairy stigma would 
all seem to facilitate ordinary pollination. Nevertheless, the very re- 
stricted style would seem to be purposely developed to counteract these 
other facilities, and we find a Pronuba associated with it, with a re- 
markably modified tongue, and with the maxillary tentacles very long 
and attenuated at the tip—structures which doubtless enable the moth 
to perform the act of pollination. I have never been able te observe 
the act, nor has anyone yet recorded either the acts of pollination or 
oviposition. There will be nothing peculiar about the latter, but I 
Shall be very glad to get actual experience in reference to the former, 
as I am satisfied that the observed facts will show, still more fully than 
in the case of Pronuba yuccasella, that the special modifications of both 
flowers and insects have gone on until the mutual interdependence has 
become absolute.* 
* Since this was written Mr. D. W. Coquillet has, at my solicitation, carefully 
watched the acts of pollination and oviposition in this species, and his accounts as 
communicated show that the actions of Pronuba maculata are substantially similar 
to those of P. yuccasella. 
