430 SYNOPTIC COLLECTION. 



become reduced in size. The body distends with unfer- 

 tilized or parthenogenetic eggs. These are laid until the 

 gall is crowded, the mother shriveling in the process, and 

 dying at its termination. Five or six generations are 

 produced parthenogenetically during the summer and the 

 number of individuals born is enormous. Since each in- 

 dividual repeats the process of making its gall-home and 

 filling it with eggs, the number of galls is also very large. 

 With the fall of the leaves in the autumn, the Gallaecola 

 that remain, quit the vines and finding their way to the 

 roots of the grape become Radicicola. It is interesting 

 to note that the newly hatched larvae which develop from 

 the eggs of the root-inhabiting type cannot be distin- 

 guished from those of the gall-inhabiting type (compare 

 fig. 7 with fig. 10), but in time the former develop tuber- 

 cles, as already stated, and the two types become distinct, 

 although so closely connected genetically that they are 

 one and the same species. 



We have here apparently the unusual phenomenon of 

 parthenogenetic individuals of two different types carry- 

 ing on the principal role in the life history of a species, 

 and the sexual females and possible males playing such 

 an unimportant part that it seems as if they could be 

 dispensed with altogether. It may be, however, that the 

 "problematical male" (fig. 6) is more necessary for the 

 continuance of the species than it appears, or possibly 

 Phylloxera has "a true sexed generation of minute, wing- 

 less " forms, as in the wooly aphis (Schizoneura lanigera 

 Hausmann) , of the apple. 1 



In one important structural feature Phylloxera differs 

 from the hop-plant aphis : it never secretes " honey dew," 

 and consequently is without the honey tubes. 



The Coccidae or scale insects are in certain ways 

 unique among insects. The newly hatched larva of the 



1 Marlatt, U. S. Dep. Agric., Div. Ent., Circular no. 20, ser. 2, 

 1897, p. 3. 



