YUCCA MOTH AND YUCCA POLLINATION. 113 
shown in the illustrations (Pl. 35, Fig. 2, ¢. c.).* The 
apical end of the egg soon enlarges (Pl. 37, Fig. 1, 2) 
and the embryo may be seen developing in it, very 
much as in the case of the similarly elongate eggs 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 punc- 
tures of the gall-flics just mentioned. Sometimes two or 
more adjacent ovules are thus affected. 
The larva hatches in about a week and will be found at a 
point from 8 to 10 ovules above or below the external punc- 
ture according as the egg was thrust above or below it. Itis 
not more than 1 mm. long and seems to live for some time on 
the juices of the degenerate and swollen ovules, but finally 
enters one that is developing, at the funicular base. So 
far as I have observed, the larva undergoes some three 
different molts, as but four different sizes of the head 
have been noticed. The general color, which is at first 
translucent white, conforms for the most part to the color 
of the tissues in which it is feeding; but becomes in time 
more yellowish, and finally, when mature, ordinarily ac- 
quires a rosy hue. The larva 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 jilamentosa. 
The number of seeds destroyed is rarely more than a dozen 
and more frequently less, and I have recorded the fact of 
* The position and development of the egg were studied in 1874, by 
Engelmann and myself (Trans. Ac. Sc. St. Louis, III, pp. 208-211) and while 
the egg, from those observations, is sometimes curled around an ovule in 
the ovarian cell, the position above described is the normal position as 
subsequent study has shown. I also gave there the duration of the 
egg state as four or five days, but it more often extends beyond a week. 
Lalso there attributed the swelling of the ovules to the action of the 
larva, but it begins before this hatches. 
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