Vegetation, as is well known, grows in a spiral direction. Speaking of animals, and in relation to the development of different forms, in a recent lecture in the hall of the Academy of Natural Sciences of Philadelphia, Miss Grace Anna Lewis remarked: "There is also a tendency to ascend in a spiral, arising from the conflict of these two forces, so that we find why animals rise in grade from lower to higher, and why they must continue to do so as long as the animal world is in existence. There also appears to be a balance of forces between the different branches, one presenting clusters different but cornplementary to the others. Thus, on the whole, the animal kingdom appears to arise by systems or pairs of branches, by what is termed a method of bichotomus branching."