Page:Popular Science Monthly Volume 41.djvu/190

From Wikisource
Jump to navigation Jump to search
This page has been validated.
178
THE POPULAR SCIENCE MONTHLY.

larging slightly toward the capitate end, which has also a slightly indurated point. It is impossible to follow it with the unaided eye, or in fact with an ordinary lens, even if the pistil be at once plucked and dissected; but, by means of careful microscopical sections, we may trace its course, as shown in Figs. 8 and 9.

The larva hatches in about a week and will be found at a point from eight to ten ovules above or below the external puncture, according as the egg was thrust above or below it. It has no pro-legs, but has well-developed thoracic legs. It matures with the ripening of the seeds, which differs in time in the different species of yucca, and also in the same species, but occupies on an average about a month in the ordinary Yucca filamentosa. The number of seeds destroyed is rarely more than a dozen and more frequently less, and I have recorded the fact of having found as

PSM V41 D190 Transverse section of yucca pistil.jpg
8.—Transverse Section of Pistil, about middle, one day after oviposition, showing (a, a) puncture of ovipositor, and (b, b) position of egg.

many as twenty-one larvae in a single pod. Just about the time the pods are hardening and ready to dehisce and the seeds have already colored, the full-grown larva bores its way out of the pod and makes its way to the ground. It remains as a larva within its cocoon during the fall, winter, and spring months, and only transforms to the chrysalis state a few days before the blooming of the yuccas. The chrysalis (Fig. 4), as shown in the figure, is armed with an acute spine on the head and with singular spatulate