1875.] Difficulties of Darwinism. 331 
hand, the Neuroptera, Orthoptera, Homoptera, and Strep- 
siptera, are devoid of venom. In certain Coleoptera, as in 
the Bembidiide, in Cychrus rostratus, and a few other Cara- 
bidz, formic acid can be ejected either as a liquid or as a 
vapour; but there is no special weapon for introducing it 
into any given object. Certain Lepidopterous larve have 
hairs, which if drawn into the lungs, or even brought in 
contact with the skin, produce painful and dangerous in- 
flammation. But even if this effect is not solely due to the 
mechanical structure of the hairs, they are not under the 
control of the larva, and are distributed at random by the 
wind. ‘There arise, then, the three following questions :— 
1. Why is the poison-faculty developed in the particular 
groups above mentioned, and not in others ? 
2. Why is the poison-apparatus seated in the head, in 
bugs, spiders, and centipedes, but in wasps and scor- 
pions in the abdomen or in the tail ? 
3. Are all the venom-bearing animals members of one 
and the same line of ascent? That they are seems 
impossible to be maintained. 
Can we construct a pedigree in which all the poisonous 
groups can be arranged in order of filiation without the in- 
tervention of non-poisonous forms? Did some articulate 
type once exist from which the bugs, the wasps, the centi- 
pedes, spiders, and scorpions have all diverged, whilst non- 
poisonous Articulata sprang from another source? If we 
take our second question into consideration the matter is 
further complicated, as we shall then have to seek a separate 
ancestry for the bugs, centipedes, and spiders on the one 
hand, and for the wasps and scorpions on the other. If no 
such lines of descent exist, we have then to explain the in- 
dependent appearance of this faculty at a number of distinct 
points in the animal kingdom, and among groups which 
cannot be shown to require it more than do several others 
not thus armed. A tiger-beetle, a dragon-fly, or a Mantis, 
able to infli@ a poisonous bite, would, in the struggle for 
existence, have enjoyed a marked advantage over others of 
its kindred. If, then, the occurrence of the venom-faculty 
be due to Natural Sele¢tion, why is it found just where it at 
present exists, and not elsewhere ? In the Hymenoptera we 
meet with further difficulties, in the sexual distribution of 
the poison-faculty, and in the fact that the organ which in 
some groups is used merely as an ovipositor, serves as a 
sting in others. In all species where the poison-power lies 
in the jaws the males and females are armed equally, as is 
also the case in the scorpion. We must, however, remember 
