1863.] 
217 
differ in 9 9 , of allied species.J On the other hand it is notorious 
that when in Neuroptera, Pseudoneuroptera and Orthoptera the % ab¬ 
dominal appendages are normal, i. e. antenniform, or degraded so as to 
be functionally useless, (Acridii,) there is scarcely any difference in 
their structure between allied species of the same genus or even of the 
same family. 
These facts lead me to suspect that generally in the Class Insecta, 
when a variation useful to % in his sexual operations does take place 
in S reproductive organs, it is often seized hold of by Natural Selec¬ 
tion to originate a new species, the less favored % % being beaten 
in the struggle for 9 9; and that species thus formed afterwards, 
'by ordinary variation and by so to speak “breeding in-and-in,” modi¬ 
fy and gradually exaggerate colorational peculiarities which were 
originally common to them and the supposed primordial form from 
which they sprang. In no other way, on the Principles of Natural 
Selection, can I account for the well-known fact of the colorational 
design or pattern being so often the same throughout a large group of 
species, though it generally differs minutely in each of these species in 
its proportions and details; while in the same group we shall find 
scarcely any structural differences, which could have been seized hold 
of by Natural Selection to originate new species, unless it be in the % 
reproductive organs. In Hetderma, for example, there are normally 
three dark stripes on the pleura of the thorax, two on what I consider 
to be the mesothoracic epimerum, and one on the metathoracic epister- 
num. Again, in Gomphus there are normally tioo dark stripes on the 
pleura, one on the mesothoracic epimerum and one on the metathoracic 
episternum. Thirdly, in Gomphus Messrs. Selys and Hagen have 
shown, that there are normally three dark stripes on each side of the 
dorsum of the thorax, or what I conceive to be the mesothoracic epis¬ 
ternum. Fourthly, in Agrion and Lestes I have shown that there are nor¬ 
mally three dark vittm on the femur, (///. pp. 282-3,) and 
I E. g. in the hymenopterous Bomhus, as observed by Audouin, quoted Westw. 
Intr. II. 281,- in the dipterous Limnohina, as observed by Osten Sacken. See 
Plates and descriptions of Plates appended to bis Paper on Limnohina in Broc. 
Phil. Acad. Sc., Aqg. 1859. I have myself observed the same thing in Locusta- 
ricE Latr. of the superior abdominal appendages or accessory reproductive 
organs. 
