the cause is not to be sought in their breathing filings, but in the sedentary and unwholesome confinement incidental to their occupation. Miners and coal-heavers are not troubled with consumption. Moreover, if the filings were the cause, all the artisans would suffer, when all breathe the same atmosphere. Secondly, while it is true that discolored lungs have been observed in some miners, it has not been observed in all or in many; whereas it has been observed in men not miners, not exposed to any unusual amount of coal-dust. Thirdly, and most conclusively, experiment has shown that the coal-dust can not penetrate to the lungs. Claude Bernard, the brilliant experimenter, tied bladder containing a quantity of powdered charcoal to the muzzle of a rabbit. Whenever the animal breathed, the powder within the bladder was seen to be agitated. Except during feeding-time the bladder was kept constantly on, so that the animal breathed only this dusty air. If the powder could have escaped the vigilance of the cilia and got into the lungs, this was a good occasion. But when the rabbit was killed and opened many days afterward, no powder whatever was found in the lungs or bronchial tubes; several patches were collected about the nostrils and throat, but the cilia had acted as a strainer, keeping all particles from the air-tubes.

The swimming apparatus of the Opalina has led us far away from the little animal who has been

feeding while we have been lecturing. At the mention of feeding you naturally look for the food that is eaten, the mouth and stomach that eat. But I hinted just now that this ethereal creature dispenses with a stomach, as too gross for its nature, and of course, by a similar refinement, dispenses with a mouth. Indeed, it has no organs whatever except the cilia just spoken of. The same is true of several of the Infusoria, for you must know that naturalists no longer recognize the complex organization which Ehrenberg fancied he had detected in these microscopic beings. If it pains you to relinquish the piquant notion of a microscopic animalcule having a structure equal in complexity to that of the elephant, there will be ample compensation in the notion which replaces it, the notion of an ascending series of animal organisms, rising from the structureless amaba to the complex frame of a mammal. On a future occasion we shall see that, great as Ehrenberg's services have been, his interpretations of what he saw have one by one been replaced by truer notions. His immense class of Infusoria has been, and is constantly being, diminished; many of his animals turn out to be plants; many of them embryos of worms; and some of them belong to the same divisions of the animal kingdom as the oyster and the shrimp-that is to say, they range with the Mollusks and Crustaceans. In these, of course, there is a complex organization; but in the Infusoria, as now understood, the organization is

extremely simple. No one now believes the clear spaces visible in their substance to be stomachs, as Ehrenberg believed; and the idea of the Polygastrica, or many-stomached Infusoria, is abandoned. No one now believes the colored specs to be eyes, because, not to mention the difficulty of conceiving eyes where there is no nervous system, it has been found that even the spores of some plants have these colored specs, and they are assuredly not eyes. If, then, we exclude the highly-organized Rotifera, or “Wheel Animalcules," which are genuine Crustacea, we may say that all Infusoria, whether they be the young of worms or not, are of very simple organization.

And this leads us to consider what biologists mean by an organ: it is a particular portion of the body set apart for the performance of some particular function. The whole process of development is this setting apart for special purposes. The starting-point of Life is a single cell—that is to say, a microscopic sac, filled with liquid and granules, and having within it a nucleus, or smaller sac. Paley has somewhere remarked that in the early stages there is no difference discernible between a frog and a philosopher. It is very true-truer than he conceived. In the earliest stage of all, both the Batrachian and the Philosopher are nothing but single cells, although the one cell will develop into an Aristotle or a Newton, and the other will get no higher than the cold, damp, croaking animal which

boys will pelt, anatomists dissect, and Frenchmen eat. From the starting-point of a single cell this is the course taken: the cell divides itself into two, the two become four, the four eight, and so on, till a mass of cells is formed not unlike the shape of a mulberry. This mulberry-mass then becomes a sac, with double envelopes or walls; the inner wall, turned toward the yelk, or food, becomes the assimilating surface for the whole; the outer wall, turned toward the surrounding medium, becomes the surface which is to bring frog and philosopher into contact and relation with the external world-the Non-Ego, as the philosopher in after life will call it. Here we perceive the first grand "setting apart," or differentiation, has taken place; the embryo having an assimilating surface, which has little to do with the external world, and a sensitive, contractile surface, which has little to do with the preparation and transport of food. The embryo is no longer a mass of similar cells; it is already become dissimilar, different, as respects its inner and outer envelope. But these envelopes are at present uniform; one part of each is exactly like the rest. Let us, therefore, follow the history of Development, and we shall find that the inner wall gradually becomes unlike itself in various parts, and that certain organs, constituting a very complex apparatus of Digestion, Secretion, and Excretion, are all one by one wrought out of it by a series of metamorphoses or differentiations. The inner wall thus passes from a simple

assimilating surface to a complex apparatus serving the functions of vegetative life.

Now glance at the outer wall: from it also various organs have gradually been wrought; it has developed into muscles, nerves, bones, organs of sense, and brain-all these from a simple homogeneous membrane !

With this bird's-eye view of the course of development you will be able to appreciate the grand law first clearly enunciated by Goethe and Von Baer as the law of animal life, namely, that development is always from the general to the special, from the simple to the complex, from the homogeneous to the heterogeneous, and this by a gradual series of differentiations.* Or, to put it into the music of our deeply meditative Tennyson,

"All nature widens upward. Evermore

The simpler essence lower lies:

More complex is more perfect-owning more
Discourse, more widely wise."

You are now familiarized with the words "differentiation" and "development," so often met with in modern writers, and have gained a distinct idea of what an "organ" is, so that, on hearing of an animal without organs, you will at once conclude that in such an animal there has been no setting apart of any portion of the body for special purposes, but that all parts serve all purposes indis

* GOETHE: Zur Morphologie, 1807. VON BAER: Zur Entwickelungsgeschichte, 1828. Part I., p. 158.