No less certain are we that the processes of digestion and assimilation have ever been unchanged. We find the same organs for these purposes as in existing animals, viz., the mouth, the stomach, the intestines, and the blood-vessels, as the coprolites and the cololites abundantly testify. We infer, therefore, with great confidence, the existence of gastric juice and bile for completing the transformation of the food into blood. Indeed, the discovery by a lady (Miss Mary Anning, of England) of that singular secretion from which the color called _India ink_ is prepared, with the ink-bag of the sepia, or loligo, in a petrified state, shows that the process of secretion existed in these ancient animals; and when we find that in all respects their structure was like that of existing animals, although some of the softer vessels have not been preserved, we cannot doubt but the entire process of digestion, and the conversion of blood into bone, nerve, and muscle, was precisely the same as it now is. In the fact, also, that we find in fossil specimens organs of respiration, such as lungs, gills, and trachea, we learn that the process of a circulation of blood, and its purification by means of the oxygen of the atmosphere, have never varied. Animal heat, too, dependent as it is essentially upon this oxygenating process, was always derived from the same source as at present. The perfectly preserved minute vessels of vegetables enable us, by means of the microscope, to identify them with the plants now alive; and they prove, too, incontestably, that the nourishment of vegetables has always been of the same kind, and has been converted into the various proximate principles of plants by the same processes. Again. We have evidence that these ancient animals possessed the same senses as their congeneric races now on the globe. We have one good example in which that most delicate organ, the eye, is most perfectly preserved. It is well known that the visual organ of insects and of crustaceans is composed of a multitude--often several hundreds or thousands--of eyes, united into one, so as to serve the purpose of a multiplying glass; each eye producing a separate image of the object observed. Such an eye had the trilobite. Each contained at least four hundred nearly spherical lenses on the surface of the cornea, united into one organ; revealing to us the interesting fact, that the relations of light to animal organization were the same in that remote era as they now are.