I take the following brief outline of the most important part of Lamarck’s theory from vol. xxxvi. of the Naturalist’s Library (Edinburgh, 1843):— “The more simple bodies,” says the editor, giving Lamarck’s opinion without endorsing it, “are easily formed, and this being the case, it is easy to conceive how in the lapse of time animals of a more complex structure should be produced, _for it must be admitted as a fundamental law_, _that the production of a new organ in an animal body results from any new want or desire it may experience_. The first effort of a being just beginning to develop itself must be to procure subsistence, and hence in time there comes to be produced a stomach or alimentary cavity.” (Thus we saw that the amœba is in the habit of “extemporising” a stomach when it wants one.) “Other wants occasioned by circumstances will lead to other efforts, which in their turn will generate new organs.” Lamarck’s wonderful conception was hampered by an unnecessary adjunct, namely, a belief in an inherent tendency towards progressive development in every low organism. He was thus driven to account for the presence of many very low and very ancient organisms at the present day, and fell back upon the theory, which is not yet supported by evidence, that such low forms are still continually coming into existence from inorganic matter. But there seems no necessity to suppose that all low forms should possess an inherent tendency towards progression. It would be enough that there should occasionally arise somewhat more gifted specimens of one or more original forms. These would vary, and the ball would be thus set rolling, while the less gifted would remain _in statu quo_, provided they were sufficiently gifted to escape extinction. Nor do I gather that Lamarck insisted on continued personality and memory so as to account for heredity at all, and so as to see life as a single, or as at any rate, only a few, vast compound animals, but without the connecting organism between each component item in the whole creature, which is found in animals that are strictly called compound. Until continued personality and memory are connected with the idea of heredity, heredity of any kind is little more than a term for something which one does not understand. But there seems little _à priori_ difficulty as regards Lamarck’s main idea, now that Mr. Darwin has familiarised us with evolution, and made us feel what a vast array of facts can be brought forward in support of it.