322 NATURAL SCTENCE. May, 
less assist fertilisation by scattering the pollen. Dried fruits of the 
previous season showed the perforations made by the escaping larve. 
Yucca austvalis, studied in south-west Texas, shows seeds 
tunnelled in the manner characteristic of the moth, the pulp being 
perforated by the escaped larve. No flowers were observed, but 
large fruits, gathered some three weeks after fertilisation, bore none of 
the constrictions or indentations which so commonly mark the 
puncture of the moth,a fact which suggests that the eggs are deposited 
in the upper part near the stigma, as was found to be the case in 
the large tree yucca, Y. brevifolia. The agent in the flowers of the 
latter is the dark-coloured Pyonuba synthetica, which is more active 
through the day than its eastern congener, and, unlike the other 
known species, slow to take flight. 
This apparent disinclination to leave the flowers may, perhaps, 
be connected with the almost constant occurrence of high winds in 
the desert, and may restrict cross-fertilisation to flowers of the same 
plant more closely than in other Yuccas, though there must be 
frequent flights from plant to plant in quiet weather, and especially 
at night, when the wind sometimes falls. Moreover, the development 
of the stigma two days before the stamens of any one flower renders 
close fertilisation, in the strictest sense, impossible. Owing to the light 
yellow colour of the pollen, in marked contrast with the smoky tint of 
the moth, laden females can be seen from a considerable distance. 
The female of most species of Pyvonuba seeks a fresh flower 
wherein to lay her eggs, preferring one in the first night of expansion, 
doubtless to ensure for her offspring a sufficient food-supply, the 
younger flowers being less likely to be already overstocked with eggs. 
This instinct is especially marked in P. synthetica, which was never 
seen to use any but the youngest flowers, while pollen-laden moths 
were repeatedly noticed forcing their way in the very narrow clefts 
between the rigid sepals of an opening bud, their flattened form 
facilitating this. When about to deposit an egg, the female runs to 
the bottom of the stamens much as _ yuccasella does, makes a rapid, 
more or less complete, circuit of their bases, and then quickly mounts 
to the very top of the pistil, and with her short, strong ovipostor cuts 
through the thin wall into the channel of the style close below the 
tip of the stigma, holding fast to the pistil meanwhile, the stamens 
being below her reach. The long extensile oviduct is then passed 
through the puncture, the egg being laid apparently within the ovary 
cell. The operation usually takes from two-and-a-half to three 
minutes longer than in other observed species. Sometimes two or 
more eggs are laid before the stigma is pollinated, but commonly, 
after laying each egg, the moth retreats to the bottom of the flower, 
and then again mounts the pistil till her head is even with the stigma, 
when she uncoils the large tentacles from their resting-place against 
her load of pollen and passes them back and forth in the stigmatic 
chamber with almost the same motion as yuccasella. The deposition 
