In vol. xx. of _Nature_, p. 528, is a very clever paper on the progression of snakes, by H. F. Hutchinson, who has evidently observed them closely. He arrives at the conclusion that they have three different modes, viz. ‘on smooth plane surfaces by means of their rib-legs;’ ... ‘through high grass by rapid, almost invisible, sinuous onward movement, like swimming;’ in climbing straight walls or ascending smooth surfaces by creating a vacuum with the ventral scales. He reminds us that cobras, kraits, the rat snake, and other slender and active kinds are constantly found on house roofs, walls, straight smooth trees, etc., and asks how they got there. He has seen the ‘abdominal scales creating a vacuum like the pedal scales of house lizards.’ He put some active little snakes on the ground, where there was no hold for the scutæ, and they ‘flew about in all directions.’ He saw that they moved on by these quick, sinuous curves—‘rapid wriggles.’ In company with my esteemed friend, Mr. Robert Chambers of Edinburgh, we made similar experiments by placing some of the smooth-scaled, active snakes on a boarded floor. Being extremely wild, they displayed their anger and skill to perfection, and literally _swam_ along, scarcely touching the floor, and so swiftly that we had difficulty in pursuing and securing them again. Some very young _Tropidonoti_ when disturbed flew or ‘swam’ about their cage in the same manner. We also saw pythons climb up a window-frame, and a corner of the room where no visible hold could be obtained; and after the example of Sir Everard Home, we allowed the reptiles to crawl over our hands, when we could feel the expansion and flattening of the body by the spreading of the ribs. I incline to agree, therefore, with the writer in _Nature_, that there is a sort of vacuum created by the ventral scales. Dr. Stradling observed that on occasions of retreat, some snakes move in such rapid and ever-varying sinuations as to baffle you completely when you attempt to lay hold of them; the part you thought to grasp is gone.[69] Such are the movements of _Pituophis_ and of _Echis_ (p. 151).