365 



widen, so that the po<l ))etomos pra<ti»"ally tliree-lobed, and the setids arc more dis- 

 tinctly in pairs, the inner sides straight and the external (juite eonvex. In ovipo- 

 sition the young fruit is i)ierced just within the ridge in tlio depn'ssion oeeupied by 

 the Btamens, 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 cas*^ 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 nnn. (Fig. 60, m,n, o) in diameter, tapering at the base and 

 enlarging 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 



Fig. 64. — a, longitudinal sectiou of pistil of Yucca filamentusa, showing {b, h) i)unctiires of Pronuba, 

 and (c, f) the normal position of her eggs in the ovarian cell; d. .section of a iiun<-tured carpel 7 days 

 after oviposition, showing the egg yet unhatched and the manner in which the ovules in the neigh- 

 borliood of puncture have been arrested in development so as to cause the constriction; e, section of 

 an older carpel, showing the larva above the original puncture ; /, a seed 13 days from oviposition, show- 

 ing voung larva at funicular base — enlargements indicated. 



lens, even if the pistil be at once plucked and dissected; birt by means of careful 

 microscopic sections we may trace its conrse. 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 dedicate 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, c). The ajiical end of the egg 

 soon enlarges (Fig. 60, h). iH'fl^ the embryo may be seen developing in it very much 

 as in the case of the similarly elongate egg of gall-flies (Cyni])idai), 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 juinc- 

 tures of the gall-flies just mentioned. Sometimes two or more adjacent ovules are 

 thus artected. 



771— No. 11 2 



