Page:Popular Science Monthly Volume 82.djvu/436

432 arachnids is identical with that of the vertebrates, and lies on the same side of the body. It affords us the fixed base line of comparison. (2) That in embryo vertebrates there are at least three pairs of primitive jaws that arise from the neural surface; they are gradually shifted from their old position to a new one on the opposite side of the head.

 showing the location of the principal organs and their probable relations; cerbl., cerebellum; ''cer. h., cerebral hemispheres; g. h., ganglion of parietal, or pineal, eye; hy., hypophysis; inf., infundibulum; ol. l., olfactory lobes; p. eye., parietal or pineal eye; s. vas., saccus vasculosus; thyr.,'' thyroid.

(3) That the old mouth and œsophagus of the invertebrates is still present, a useless, heretofore unintelligible, rudiment, in its proper place in the floor of the brain of all vertebrates. This old passageway