365 
widen, so that the pod becomes practically three-lobed, and the seeds are more dis- 
tinctly in pairs, the inner sides straight and the external quite convex. In ovipo- 
sition the young fruit is pierced just within the ridge in the depression occupied by 
the stamens, and almost always on the side of one of the primary or deeper divisions 
where the walls are thinnest, so that the ovipositor enters the ovarian cell at the 
external or rounded side of an ovule and does not ordinarily touch the ovule itself. 
Rarely, however, the ovipositor penetrates the ridge and passes between two of the 
ovules, or sometimes even penetrates one, this last case being, however, quite excep- 
tional. 
The egg is an extremely delicate, thread-like structure, averaging 1.5 mm. in 
length and less than 0.1 mm. (Fig. 60, m,n, 0) in diameter, tapering at the base and 
enlarging slightly toward the capitate end, which has also a slightly indurated 
point. Itis impossible to follow it with the unaided eye, or in fact with an ordinary 
xT i 
Fic. 64.—a, longitudinal section of pistil of Yucca filamentosa, showing (b, 6) punctures of Pronuba, 
and (c,¢c) the normal position of her eggs in the ovarian cell; d, section of a punctured carpel 7 days 
after oviposition, showing the egg yet unhatched and the manner in which the ovules in the neigh- 
borhood of puncture have been arrested in development so as to cause the constriction; e, section of 
an older carpel, showing the larvaabove the original puncture; jf, aseed 13 days from oviposition, show- 
ing young larva at funicular base—enlargements indicated. 
- 
lens, even if the pistil be at once plucked and dissected; but by means of careful 
microscopic sections we may trace its course. From the position assumed by the 
moth, the ovipositor punctures the pistil somewhat obliquely, but as the egg is 
much longer than the diameter of the ovarian cell, the delicate oviduct of the moth 
bends and then runs vertically along the inner part of the cell next the placenta, 
and leaves the egg extending in this longitudinal direction along some seven or 
eight ovules, as shown in the illustrations (Fig.64¢,¢c). ‘The apical end of the egg 
soon enlarges (Fig. 60,), and the embryo may be seen developing in it very much 
as in the case of the similarly elongate egg of gall-flies (Cynipide), though the 
pedicel does not shorten, as observed in these last. Segmentation is noticeable on 
the second day, and the Yucca ovule at once begins to swell and enlarge, the irritation 
(doubtless mechanical) influencing the plant tissue much as in the case of the pune- 
tures of the gall-flies just mentioned. Sometimes two or more adjacent ovules are 
thus affected. 
T7I—No. 11——2 
