1864.] 
449 
parthenogenesis the spring brood of spongijica in the following year. 
It is scarcely necessary to add, that the facts utterly overthrow this 
hypothesis. On the subject of Dimorphism, see my Paper on Pseu- 
doneuroptera. (i^roc. Ent, Soc. Philad. II, p. 221—2.) 
The differences between these two dimorphous forms are so striking, 
that at the very first glance every entomologist who saw them for the 
first time would pronounce them to be distinct species, and there are no 
intermediate grades of any consequence. I have now before me 6 S , 
5 9 of spongijica, and 30 9 of aciculata, and the following differences 
are observable:— 
1st. The fovea at the base of the scutel is twice or thrice as deep in 
spongiji.ca, and the longitudinal carina which bisects it is twice or 
thrice as lofty. 
2nd. In spongijica there are three deep and wide, transversely cor¬ 
rugated, longitudinal striae or sutures in front of the scutel, one central 
one extending nearly to the collare, but becoming narrower as it ap¬ 
proaches it, and two divergent lateral ones fading out as they approach 
the humerus. In aciculata it is only in particular lights that traces of 
these striae are discoverable, and they do not extend nearly so far for¬ 
wards. 
3rd. In aciculata on each side of the notum, beginning at the col¬ 
lare and terminating suddenly about half-way to the scutel, is an almost 
invariably conspicuous, obtuse, glabrous carina, each parallel with the 
other and distant from the other about as far as the two posterior ocelli 
are. In spongijica it is only in two or three specimens and in certain 
lights, that faint traces of these two carinse are discoverable. 
4th. In aciculata the mesonotum is very finely aciculate, or covered 
with fine regularly parallel rugae before the scutel, except in two or 
three specimens where it is somewhat irregularly but very finely rugose. 
In spongijica, it is very coarsely rugose. There is some little varia¬ 
tion in both these two forms, but comparing the most coarsely sculp¬ 
tured aciculata with the most finely sculptured spongijica, the rugosi¬ 
ties are at least twice as coarse in the latter, i. e. each rugosity is twice 
as wide. 
5th. The sculpture of the rest of the thorax and also of the head is 
about twice as coarse in spongijica as in aciculata. 
6th. The body of aciculata is uniformly black except that the abdo- 
