204 T. H. Morgan 
A microscopic study of the reproductive organs showed that 
these were so immature that [ was unable to tell whether the 
individual would be male, sexual female, or parthenogenetic. 
In only a few cases as stated above have the sexual forms of the 
American species of Phylloxerans been described. ‘This is to be 
regretted because it leaves our knowledge of the life-cycle incom- 
plete at a critical point, and also because the sexual forms are more 
different in different species than are the parthenogenetic individ- 
uals, and therefore are of the utmost importance in the classifica- 
tion and identification of this difficult group. By means of the 
method here described one may obtain an abundance of material 
that would be in some cases very difficult to find under natural 
conditions. 
I have given figures in Plate I of the sexual forms male and 
female of the two species dealt with at length in this paper, and 
also of the sexual ( ?) forms of three other species found in the vicinity 
of Woods Hole, Mass. In the latter only one form exists, as I have 
stated. Sections show that the reproductive organs are in a rudi- 
mentary stage and while I have not made very careful study of 
them, still I have not been able to distinguish the male from the 
female organ at this time. ‘This fact is all the more striking when 
it is recalled that in the other species the male organ forms a 
conspicuous feature even of the early development and the large 
testes of the just hatched male contain ripe sperm. In the female, 
too, the egg at the time of hatching almost completely fills the body 
and is so conspicuous that it can be seen through the transparent 
wall of the body. 
It remains for the future to discover the fate of these sexual ( !) 
forms of the other species. ‘The long proboscis may indicate 
that they live on the bark of the trees. If so their small size would 
make it difficult to detect them. [ enclosed in a cloth baga branch 
of a tree and placed within it many ripe galls. A subsequent 
examination of the branches failed to reveal any Phylloxerans, but 
the conditions were not very favorable. 
The idea suggests itself to any one familiar with the facts here 
recorded that the third generation of these species is not a sexual 
generation at all, but one destined to continue the race by partheno- 
