The true jaws of the carpenter bees are not any more prominent or better adapted for making clean-cut perforations than those of the humble bees; but behind the jaws there is a pair of long, sharp-pointed, knife-like, jointed organs (maxillae) which seem to be exclusively used on all ordinary occasions in making perforations. The inner edges of these maxillae are nearly straight, and when brought together they form a sharp-pointed, wedge-shaped, plow-like instrument which makes a clean, narrow, longitudinal slit when it is inserted in the flower and shoved forward. The slits made by it are often not readily seen, because the elasticity of the tissues of some flowers causes them to partially close again. When not in use the instrument can be folded back, so that it is not conspicuous. The ordinary observer usually sees no difference between the humble bees and the carpenter bees, but they may be readily distinguished by a little close observation. [Illustration: THE PERFORATION OF FLOWERS. 1. Xylocopa and heads of male and female. 2. Bombus and head. 3. Dicentra spectabilis, showing punctures. 4. Ribes aureum. 5. Ligustrum Ibota. 6. AEsculus glabra. 7. Lonicera involucrata. 8. Caragana arborescens. 9. Andromeda Japonica. 10. Buddleia Japonica. 11. Mertensia Virginica. 12. Rhododendron arborescens. 13. Corydalis bulbosa.] No doubt, in some of the recorded cases of perforations, carpenter bees have been mistaken for humble bees. The heads of all our Northern humble bees are rather narrow, retreating from the antennae toward the sides, and with a more or less dense tuft of hair between the antennae. The abdomen, as well as the thorax, is always quite densely covered with hair, which may be black or yellowish or in bands of either color. With possibly one or two exceptions, the only species I have seen doing the puncturing is Bombus affinis, Cresson. The carpenter bees (Xylocopa Virginica) of this region have the head very broad and square in front, and with no noticeable hair between the antennae. The heads of the male and female differ strikingly. In the male the eyes are lighter colored and are hardly half as far apart as in the female, and the lower part of the face is yellowish white. The female has eyes smaller, darker, and very far apart, and the whole face is perfectly black. The abdomen is broad, of a shining blue-black color, very sparsely covered with black hairs, except on the first large segment nearest the thorax. On this segment they are more dense and of the same tawny color as those on the thorax. But it is particularly from the character of the head that the amateur observer of the perforators may soon learn to distinguish between a Xylocopa and a Bombus as they work among the flowers. It is also interesting to know that the Xylocopas are not so inclined to sting as the humble bees, and the males, of course, being without stinging organs, may be handled with impunity.