6 i8 
THE STUDY OF INSECTS . 
the characteristics of Neuroterus , but have been classed in 
another genus under the name Spathegaster (Spath-e-gas'ter). 
These in turn lay eggs which develop into gall-flies like their 
grandparents, i.e., a species of Neuroterus . Not only, says 
Mr. Adler, do the two generations live in galls differing in 
form, color, and situation, and the insects exhibit among 
themselves differences of size, proportions, and structure, but 
what renders the contrast more striking is that the Neu¬ 
roterus generation is only represented by females, whilst the 
Spathegaster generation presents individuals of both sexes. 
Although alternation of generations occurs in many 
species of the Cynipidse, it is believed that there are other 
species in which the parthenogenetic form exists alone; that 
is, the species reproduce continuously without any males ap¬ 
pearing. There can be no doubt that these parthenogenetic 
species have descended from species consisting of both sexes. 
Still, it is said that no case is now known of a bisexual form 
existing alone; each bisexual species is merely a link in a 
cycle containing a parthenogenetic generation. 
The members of this family infest many kinds of plants, 
but their galls occur most abundantly on oaks. Among the 
more conspicuous species are the following: s 
The Fibrous Oak-apple, Amphibolips coccinece (Am-phib'- 
o-lips coc-cin'e-ae).—There are several large, spherical galls, 
common on oaks, which have received the name of oak-apples. 
These galls resemble each other quite closely in their ex¬ 
ternal appearance, but differ much in their internal struc¬ 
ture. The one which we name the Fibrous Oak-apple is 
represented by Figure 746. In the centre of the gall there is 
a small, hollow kernel, in the cavity of which the gall-fly is 
developed. The space between this kernel and the dense 
outer layer of the gall is filled with many fibres, which radi¬ 
ate from the kernel. This gall is found on the scarlet oak, 
and varies in size from three fourths inch to two inches in 
diameter. 
The Spongy Oak-apple, Amphibolips spongifica (A. spon- 
