_Embryonic Development._—Man is developed from an ovule, about the 125th of an inch in diameter, which differs in no respect from the ovules of other animals. The embryo itself at a very early period can hardly be distinguished from that of other members of the vertebrate kingdom. At this period the arteries run in arch-like branches, as if to carry the blood to branchiæ which are not present in the higher vertebrata, though the slits on the sides of the neck still remain (_f_, _g_, fig. 1), marking their former position. At a somewhat later period, when the extremities are developed, “the feet of lizards and mammals,” as the illustrious Von Baer remarks, “the wings and feet of birds, no less than the hands and feet of man, all arise from the same fundamental form.” It is, says Prof. Huxley,[12] “quite in the later stages of development that the young human being presents marked differences from the young ape, while the latter departs as much from the dog in its developments, as the man does. Startling as this last assertion may appear to be, it is demonstrably true.” As some of my readers may never have seen a drawing of an embryo, I have given one of man and another of a dog, at about the same early stage of development, carefully copied from two works of undoubted accuracy.[13] [Illustration: Fig. 1. Upper figure human embryo, from Ecker. Lower figure that of a dog, from Bischoff. _a._ Fore-brain, cerebral hemispheres, &c. _b._ Mid-brain, corpora quadrigemina. _c._ Hind-brain, cerebellum, medulla oblongata. _d._ Eye. _e._ Ear. _f._ First visceral arch. _g._ Second visceral arch. H. Vertebral columns and muscles in process of development. _i._ Anterior ┐ │ extremities. K. Posterior ┘ L. Tail or os coccyx.]