In colour a rattle is of a dark brown, or dull rusty black, occasionally lighter when fresh and uninjured, and then more plainly displaying its horny texture. In the Mexican rattle (p. 296) the links were semi-transparent; sufficiently so to enable us to trace the form of the interior links if held against the light. This afforded an admirable opportunity to comprehend the structure and the production of the sound, which is simply and truly a rattling of these loosely-fitting links as they are partially embraced, each one by the previous link. That is to say, each new link grows up into its predecessor, pushing it forward towards the tip of the rattle. Through this unusually clear rattle you can trace each link passing up and fitting into the preceding (prior) one, just as so many thimbles or cups would fit into each other. Only, in the case of thimbles or cups, there is nothing to keep them in place, and the slightest shake would detach the whole pile; whereas the lobes or bulging sections of each link prevent any such detachment in a rattle, except by force or accident. The next is the rattle of a small Oregon snake. This, as is observable, is old and very much worn; so much so, indeed, that one has to handle it with care. It is, however, pulled apart intentionally to show that the links vary in form from those of the tapering specimen. Any rattle can thus be separated without much effort, as, owing to the elasticity of the substance, not much resistance presents itself. The links are just loose enough to produce that sibilant effect, like the rustling of dry leaves, or of ripe beans in a pod; or still more, like the seed vessel of our own native plant the Yellow Rattle, _Rhinanthus Crista galli_, and the American ‘Rattle-Box,’ _Crotalaria sagittalis_. [Illustration: Small divided rattle.] Yet just so securely fitting it is as to permit of the continual vibration without loss of links. What we _see_, therefore, is only the base or lower lobe of each joint, the rest running up into the next two or even three bases, as may be traced in the section here given. [Illustration: Section of rattle.] In reading about the construction of a rattle, some perplexity may occur from the various adverbs before, behind, first, last, previous link, etc., some referring to age, others to place. Descriptions of the rattle met with in popular physiological works prove the above perplexities, and verify what is so often demonstrated, viz. the ‘inability of unscientific persons to read scientific matter correctly.’ The ‘last’ link means the one last grown, not the end one of the tail; ‘pushing the preceding one _forward_’ is not towards the _head_ of the reptile, but literally _outward_ and _backward_ towards the tip of the tail. ‘Previous’ may mean in time, or the age of the link, or it may mean position; but a knowledge of the development assists the comprehension of such passages.