An eminent French professor of the art of sleight-of-hand has defined the leading principle of jugglers to be that of "appearing and disappearing things;" and this is the best definition that occurs to me of one method of reasoning largely used by Haeckel, and of which we need to be on our guard when we find him employing, as he does in almost every page, such phrases as "it cannot be doubted," "we may therefore assume," "we may readily suppose," "this afterward assumes or becomes," "we may confidently assert," "this developed directly," and the like, which in his usage are equivalent to the "_Presto!_" of the conjurer, and which, while we are looking at one structure or animal, enable him to persuade us that it has been suddenly transformed into something else. In tracing the genealogy of man he constantly employs this kind of sleight-of-hand in the most adroit manner. He is perhaps describing to us the embryo of a fish or an amphibian, and, as we become interested in the curious details, it is suddenly by some clever phrase transformed into a reptile or a bird; and yet, without rubbing our eyes and reflecting on the differences and difficulties which he neglects to state, we can scarcely doubt that it is the same animal, after all. The little lancelet, or _Amphioxus_ (see Fig. 1), of the European seas--a creature which was at one time thought to be a sea-snail, but is really more akin to fishes--forms his link of connection between our "fish-ancestors" and the invertebrate animals. So important is it in this respect that our author Waxes eloquent in exhorting us to regard it "with special veneration" as representing our "earliest Silurian vertebrate ancestors," as being of "our own flesh and blood," and as better worthy of being an object of "devoutest reverence" than the "worthless rabble of so-called 'saints.'" In describing this animal he takes pains to inform us that it is more different from an ordinary fish than a fish is from a man. Yet, as he illustrates its curious and unique structure, before we are aware, the lancelet is gone and a fish is in its place, and this fish with the potency to become a man in due time. Thus a creature intermediate in some respects between fishes and mollusks, or between fishes and worms, but so far apart from either that it seems but to mark the width of the gap between them, becomes an easy stepping-stone from one to the other. [Illustration: FIG. 1. The Lancelet (_Amphioxus_), the supposed earliest type of vertebrate animal, and, according to Haeckel, the ancestor of man. The figure is a section enlarged to twice the natural size. _a_, mouth; _b_, anus; _c_, gill-opening; _d_, gill; _e_, stomach; _f_, liver; _g_, intestine; _h_, gill-cavity; _i_, notochord, or rudimentary back-bone; _k_, _l_, _m_, _n_, _o_, arteries and veins.]