YUCCA MOTH AND YUCCA POLLINATION. 143 
tics of the species are, however, well adapted to the work 
it has to perform in the densely packed and but partially 
opened flowers of this Yucca with their denser petals and 
firmer pistils ; for all the parts which are representative of 
the other species of Pronuba are here more stout, and the 
denuded and flattened body is well suited to creeping 
between the flowers. There is no question but that the 
tree Yuccas represent an ancient type of our flora, and. 
Pronuba synthetica may also be looked upon as an ancient 
type of our Lepidopterous fauna. That it should have so 
many striking peculiarities that recall insects of other 
orders, is, therefore, very suggestive. I was very anxious 
to obtain the larva and chrysalis of this species, and the 
following year Mr. Koebele, at my request, revisited the 
tree Yuccas and succeeded in May, 1888, in obtaining 
infested fruit. As soon as this was received, the 
larve left the pods and entered the ground, some of them 
forming cocoons almost identical in appearance with that 
of yuccasella. Others remained in the larva state, without 
forming cocoons. Indeed, one peculiarity noticeable was the 
great length of the larval life, as a few had not yet formed 
their cocoons by the end of 1889, or more than a year 
from the time they were received, while one was living and 
unchanged, in its cocoon, in August, 1891, or nearly two 
years and a half from the time it left the fruit. However, 
most of those that were reared to the imago state, whether 
by Mr. Koebele in California or at Washington, issued the 
following March or April. These facts would indicate that 
while normally the moth is produced the ensuing year, yet 
belated individuals may not issue from the ground until the 
second or even the third year, and I have been informed 
that it is not an uncommon thing for Yucca brevifolia to 
produce no flowers over large districts during some years. 
The tendency to retardation in development is, under these 
circumstances, advantageous to the species. 
