There are few more puzzling questions than those which arise over these eccentricities of structure; they seem to have no relation to any habits of the creatures' lives so far as we can judge, neither can one suggest any useful purpose which they can serve. In some groups the males of all the species seem built on one regular plan—in others the males of each species seem to vie with the next as to what eccentricity of structure in antennæ or legs or apex of the body it can exhibit. In numbers, the males probably considerably exceed the females, and are far more frequently met with, as they seem to be less particular as to weather, and not being intent on obtaining food for their offspring they fly about more casually, and certainly are more in evidence generally.
The great difference in structure, etc., between the males and females makes the work of pairing the sexes very difficult, especially in those genera where the males and females appear together only for a few weeks, as is the case in Halictus and Sphecodes. If one visits a locality in the spring one may catch any number of females of Halictus, but no males appear till the late
summer or autumn, and, unless one visits the same spot again when both sexes are out, it is impossible to associate males and females. I have at the present moment in my collection several males, which, being in doubt about myself, I have communicated to continental authorities, who have returned them to me as possibly the male of so and so! and we shall have to remain in uncertainty about them till some one happens to take both sexes together, when the mystery will be solved.
In time of appearance the males always precede the females—in burrows, such as those of the leaf-cutting bees, etc., it may seem puzzling as to how this is arranged, as one cell is placed over the other so that those lower down in the tube cannot pass those higher up. This difficulty is got over by the arrangement that the first eggs laid by the mother bee are female and the last male, so that those at the top belong to this latter sex; these emerge as soon as the warmth of the sun is great enough to energize them sufficiently to break through their cell covering, when they emerge and wait for the appearance of their females. The males of
some species of Andrena seem to take great pleasure in flying rapidly up and down hedgerows, hardly ever settling, and apparently far away from their females, which are probably pollen collecting in dandelions or some such flowers in the neighbourhood.
THE VAGARIES OF COLOUR AND STRUCTURE IN THE SEXES
As a rule the male is rather smaller and especially slenderer than the female, but there are notable exceptions; in one genus of the fossors, Myrmosa for instance, the male is many times larger than the female. In this case the male is winged and the female is wingless. Also, if there is a difference in brightness of coloration between the sexes, as a rule the male is duller than the female—this is especially the case among the bees—but if there is any eccentricity in the form of the limbs it is almost sure to occur in the male, and I think one would not go far wrong in saying that when peculiar features occur in the female, the reason for them is more or less apparent, whereas for the eccentricities of the male there really often seems to be no assignable cause. These male eccentricities are often exceedingly marked. A very good