YUCCA MOTH AND YUCCA POLLINATION. 125 
from the septal glands. Small beetles and flies were very abundant in 
the flowers and seem to feed on the pollen, collecting on the anthers for 
that purpose. The former may also gnaw the papille of filaments, for 
the stamens become sodden and wilt within a day or two when these 
beetles are present —but I have not seen the latter gnawing at them. 
In their operations upon the anthers these little insects sometimes dis - 
lodge a ball of pollen which falls down. In one flower with horizontal 
pistil such a lump was seen on the green style near its apex; but the 
probability of any pollen falling in this manner where it could develop 
its tubes in the stigmatic chamber, is very slight except in case of a pos- 
sible deformity of the pistil by the reflection of the upper stylar lobe — 
thus opening the chamber above — or the upbending of the style so that 
the opening was directed toward the uppermost stamen. Aphides and 
Coccinellids were of course very abundant, but play no part whatever in 
pollination. A fair number of capsules were set this year, and all I saw 
were found to contain larve of Pronuba or to show the characteristic 
scars or constrictions where the moth had pierced the ovary. 
“‘ Prodoxus was very abundant, and I send you a number of both sexes. 
Nos. 19, 32 and 33, [all of Prodoxus decipiens] were seen ovipositing in 
stem of angustifolia, head upward, the abdomen being worked much as 
with Pronuba. Numerous Prodoxus were seen flying from flower to 
flower very actively, and the sexes were seen in coitu in a flower, the 
abdomens working much as in ovipositing. The female in the cases 
watched by me when ovipositing in the stem, crept up a short distance 
before laying each new egg. 
“‘ Apropos of Meehan’s idea that the Pronuba moth close-fertilizes the 
flower, I have seen females when undisturbed go from fiower to flower 
here, and several times in the mountains a female was seen, without 
having been disturbed, to fly off horizontally from a plant on the steep 
mountain side, with every evidence of the necessity for a long flight be- 
fore finding another Yucca.”’ 
We have in the structures and functions which are so 
characteristic of this Yucca Moth, admirable adaptations of 
means to an end, whether for pollinizing the plant or pro- 
viding for a future generation. The Pronuba larva rarely 
destroys more than a dozen of the seeds, so that several may 
develop within a single pod and yet leave many perfect 
seeds, while, for the reasons already stated, we occasionally 
have pods without a trace of the insect. 
There is between Pronuba and its food-plant a mutual 
interdependence which excites our wonder, and is fraught 
with interesting suggestions to those who are in the habit 
of reasoning from effect to cause. Whether we believe, as 
