222 
[October 
species of CoUas, (See Proc. Ent. Soc. Phil. I. p. 349-51,) is nothing 
but a phase of Dimorphism; and the orange-colored 9 9 of Agrion 
Ramhurii are perhaps referable to the same class of facts, for I do not 
remember ever to have seen any intermediate grade between the blue 9 
and the orange-colored 9 . Thirdly, in the coleopterous genus Sia- 
gonium and its allies, where the % head is armed with horns, we are 
told by Westwood that ‘‘ these cornuted individuals appear to be of 
two distinct kinds,” some with large and’ some with small horns, and 
that “ out of 50 S % of Siagonmm he was not able to find a single in¬ 
dividual intermediate between the two kinds”; (Introd. I. p. 172,) 
which is a clear case of % dimorphism. Fourthly, it has long been 
known that certain species of Orthoptera, Hymenoptera and especially of 
Heteroptera and Homoptera sometimes occur in the % 9 imago state 
with very short wings and sometimes with long ones, without any inter¬ 
mediate grades, and that other species are in the % imago sometimes 
fully winged but generally apterous, without any intermediate grades, 
an instance of which, in the Ichneumonide genus Pezoniachus, I 
have recorded in my Essay on Insects injurious to Vegetation in Illi¬ 
nois (p. 369.) Fifthly, in Cynipidae I have some very strong proof, 
which at some future time I shall offer to the world, that Hartig’s 
agamous species, which exist only in 9 sex, are mere dimorphous forms 
of bisexual species.* In the Vegetable Kingdom it appears that there 
are even trimorphous species, and similarly in Formicidae the genus 
Atta, a species of which commonly occurs in Illinois, has one kind of 
neuters with heads of the ordinary proportions, and another kind with 
heads as bulky as the remaining part of their bodies, with no interme¬ 
diate grades whatever, as I have repeatedly observed. A phenomenon 
apparently of the same kind occurs in Termes, but as in Pseudoneurop- 
tera the larva and pupa resemble the imago and are active, and as the 
so-called “ nasuti” may possibly be larvae, the case is not so strong a 
one. It has often been said that there are also two distinct sizes 
of neuters belonging to the hymenopterous genus Formica, but my 
experience is that here all the intermediate sizes coexist in the same 
See on this subject Baron Osten Sacken’s Papers on N. A. Cynipidoe, Proc. 
Ent. Soc. Phil. I. pp. 49—50 and 248—249. Brulle dismisses this physiologi¬ 
cally important and very remarkable subject in a dozen lines. Suites a Buffon. 
Hymenopt. IV. p. 632. 
