Wings in the Coleoptera. itt 
stage, have no purpose to serve is perfectly clear. We have 
therefore to do with an organ which either will at some time 
arrive at full development and function, and is consequently 
advancing, or which was at an early period well developed 
and in use as an organ of flight, and has consequently re- 
trograded. 
That it is not an advancing organ, but one in course of dis- 
appearance, is shown most decidedly by the circumstance that 
this, like all retrogressive organs, does not, like those in 
full function, increase with the development of the individual, 
but, on the contrary, diminishes. 
We are therefore justified in assuming that Niptus holo- 
leucus once bore well-developed hind wings, and that these 
gradually became aborted in consequence of disuse, until they 
were finally thrown back into the young stages, and some day 
will disappear even from these stages. In other wingless 
beetles this period may have already occurred. 
While in other cases the hind wings make their appearance 
nearly at the same time as the fore wings, we have seen that 
the aborted hind wings in Neptus originate much later than 
the equivalent organs which attain development, namely the 
fore wings. ‘This circumstance seems to show that rudimen- 
tary organs are not only thrown back to the younger stages, 
but that, in many cases also, the period of their appearance is 
much later than with the equivalent well-developed organs. 
They are consequently, if | may so express myself, straitened 
on two sides. IL do not know whether other rudimentary 
organs, such, for example, as the upper incisors of the Rumi- 
nants, which never break through, make their appearance much 
later than the well-developed lower ones. 
This abortion of an organ brings after it other transforma- 
tions of the body. Without the hind wings the beetles can- 
not fly. It is therefore not necessary for them to be able to 
spread out the elytra, the latter rather remain permanently 
lying upon the back. What is the consequence? The two 
elytra grow together to form a firm dorsal shield, such as we 
find in nearly all beetles which are entirely destitute of hind 
wings. At the same time the elytra become convex and 
bend round at the sides, so that they embrace the abdomen. 
In consequence of the disappearance of the wing-muscles, the 
thorax becomes altered. ‘lhe body acquires quite a different 
form ; new forms are produced which we call species. 
