The accompanying illustration shows the tracheæ of three well-known creatures. The left-hand figure is the trachea of an Ox, the central figure that of a Pig, and the right-hand figure that of a Goose. Mr. Tuffen West, who made the drawings, sent with them the following remarks:-- “The tracheæ of animals furnish some very interesting examples of variation in the form and arrangement of the rings. Their purpose, perhaps, one can but guess at in some cases; but doubtless, as being works of the Master Builder, careful study would be repaid. “In the Ox the rings are very strong and close, and in form like a horse-shoe with the ends approximated. “In the Pig the incomplete rings are broad at one part, and narrow on the opposite side, with a tendency to spiral arrangement. I imagine that this would make a very rigid tube, and, indeed, it feels so in the hand. “Then, in the Goose, the narrowed lower part is that which is figured just before the trachea reaches the sternum. The (complete) rings are twice as broad in one half as in the other, and by the alternate disposition of these differing widths, a tube is formed of great flexibility fore and aft, but almost absolutely rigid in the lateral direction. This seems to be so marked an evidence of design as to be calculated to greatly raise our admiration.” [Illustration: RINGED TISSUES OF SUGAR-CANE] [Illustration: VEGETABLE SPIRAL TISSUES TENDING TO RINGS.] * * * * * WE have seen several examples of ringed tissues tending to the spiral form, and it is but natural that we should expect to find spiral tissues tending to the ring. In the accompanying illustration the two left-hand figures represent the curiously modified ringed tissue which is to be found in the sugar-cane, the left-hand figure being much more magnified than the other. The other figures represent four examples of vegetable spiral tissues, in which it will be seen that there is a tendency to form rings, and that if a number of rings were substituted for the spiral, and the object viewed in a slanting direction, it would be almost impossible to distinguish between the ring and the spiral. Among the most remarkable of these examples are the two right-hand figures. That on the extreme right represents a spiral vessel taken from the so-called root, or “rhizome,” of the Water-lily, and the other is a similar vessel taken from a branch of the Yew-tree. It has been suggested that to this spiral structure is due the proverbial elasticity of the yew-tree, which has from time immemorial rendered it the best wood for the manufacture of bows. DIVING AND DIVERS. It has already been mentioned that the flexible tubes used by modern divers are constructed on the model of several structures belonging to the animal and vegetable kingdoms. We will now see how they are utilised. * * * * *