RILEY OVIPOSITION OF THE YUCCA MOTH. 209 



"This carrying of the pollen to the stigma generally follows every act 

 of oviposition, so that, where ten or a dozen eggs are consigned to a sin- 

 gle pistil, the stigma will be so many times be-pollened. The ends of the 

 tentacles, which are most setose and spiny, and which are always curled 

 into the pollen-mass when not uncoiled, must necessarily carry a number 

 of pollen grains each time pollination takes place; and I have noticed a 

 gradual diminution in the size of the collected mass, corresponding, no 

 doubt, to the work performed, which is indicated by the rubbed and worn 

 appearance of the individual — the freshest specimens always having the 

 largest loads. 



" While oviposition is generally followed (and not preceded, as I for- 

 merly supposed) each time by pollination, yet the former sometimes takes 

 place twice, thrice, or oftener, without the latter being performed ; and I 

 suspect that the converse of this is equally true. 



it * * * J have little doubt but that the egg increases in bulk, before 

 hatching, under the influences of impregnation and endosmosis, and Dr. 

 Engelmann tells me that he has been able to trace the embrj'o larva under 

 the extremely delicate egg-covering, and to observe it curled up at the 

 anterior end of the egg, which greatly enlarges. This larva hatches on 

 the fourth or fifth day after the laying of the egg, and usually commences 

 feeding between two ovules, which, in consequence of its action, swell 

 abnormally. Thus, in making a longitudinal section of the fruit, these 

 swollen ovules often indicate the presence of the. worm where it would 

 otherwise be overlooked while very small. 



"Though oviposition generally takes place in the manner described, the 

 moth head outwards and straddling two stamens, an entirely opposite 

 position must sometimes be assumed, since larvje and punctures are not 

 unfrequently found in the upper part of the fruit, especially where a single 

 one is stocked with ten or a dozen larvae, as is sometimes the case.* As 

 the fruit enlarges, the mouth of the puncture forms a slight, discolored 

 depression, more noticeable in some varieties than in others ; but the pas- 

 sage-way becomes obliterated. 



"My observations this summer might be extended much in detail. They 

 have convinced me more than ever that Pronuba is the only insect by the 

 aid of which our yuccas can be fully fertilized ; for I have studied this fer- 

 tilization diligently night after night, without seeing any other species go 

 near the stigma. The stigmatic opening closes after the first night, and I 

 know of no crepuscular or nocturnal species which could collect the requi- 

 site amount of pollen and bring it so to bear on the stigma that each ovule 

 would receive the influence of a pollen grain. The species already enu- 

 merated! as frequenting yuccas are mostly diurnal and have nothing to do 

 in the work ; and wherever I have excluded the moth from the flowers, by 

 enclosing the latter with netting, no fruit has been produced. I am there- 



* 1 have counted as many as twenty-one larva: in a single capsule of what is apparently 

 T. jlaccida. ^ Ante,-^.<f). 



iii — 14 [April as, 1874.] 



