The Bogus Yucca 3fofh.'^. 



97 



spine, l)ut the barest trace of dorsal spines on the alxloniinal 

 joints. It issues partly from the stem in giving out the motli. 

 As I have elsewhere remarked : 



'■ Who, studying these two species in all their characters and 

 hearing, can fail to conclude that, notwithstanding tlie essential 

 differences that distinguish them not only specifically, l)ut ge- 

 nerically, tliey are derived from one and the same ancestral form ? 

 PrDUuha, depending for its existence upon the pollination of the 

 tlowcr, is profoundly modified in the female sex in adaptation 

 to the peculiar function of pollination. Prodoxus, dwelling in 

 tlic fh'sli of the fruit or in the fiower-stem and onlv indireetlv 



!^ 



7,- 



[f 



Fig. 12. — Puonoxfs df.cipif.xs: a, larva: ';, head tVom above : c, d, left jaw arid antenna; 

 e. pupa ;/, infested !stem eut open to show the burrows, casting.s, cocoons, and pupa 

 shell ;/i)-alI enlarged liut f, the hair-line between a and e showing natural length. 



depending upon the fructification of the plant, is not so modified, 

 hut has the ordinary characters of the family in both sexes. In 

 tlie former the larva quits the capsules and liurrows in the 

 ground ; it has legs to aid in its work, while the chrysalis is 

 likewise beautifully modified to ada[)t it to pr3'ing through the 

 ground and mounting to the surface. The latter, on the con- 

 trary — never quitting the stem — has no legs in the hirva state) 

 and in tlie chrysalis state is more particularly adajitcd. I>y the 



l:{— Hkil. Si.i'.. Wash.. Vnr.. VII. ISO".,'. 



