. Evolution and disease . ^ it pre-sents the structural details found in functional eyes,such as cornea, lens, retina, pigment, &c. (fig. 22).. Fig. 21.—Lateral view oi tiic i)rain of Sphenodon, showingthe relation of the pineal eye, P ; the cerebrum, C; and themedulla, M. (After Baldwin Spencer.) Spencer is of opinion that this suppressed eye repre-sents the unpaired eye of larval Tunicata. There isgood evidence that it was highly developed in extinctamphibia {LabyrintJwdontd), and was probably a sense-organ in animals of pre-tertiary periods. It is not unreasonable to suppose that the gradua
. Evolution and disease . ^ it pre-sents the structural details found in functional eyes,such as cornea, lens, retina, pigment, &c. (fig. 22).. Fig. 21.—Lateral view oi tiic i)rain of Sphenodon, showingthe relation of the pineal eye, P ; the cerebrum, C; and themedulla, M. (After Baldwin Spencer.) Spencer is of opinion that this suppressed eye repre-sents the unpaired eye of larval Tunicata. There isgood evidence that it was highly developed in extinctamphibia {LabyrintJwdontd), and was probably a sense-organ in animals of pre-tertiary periods. It is not unreasonable to suppose that the gradualdevelopment and greater utility of the lateral eyeshave led to the suppression of the median eye. Although the pineal body (regarded by Descartes asthe seat of the soul) in man is clearly vestigial, it is 44 EVOLUTION AND DISEASE. by no means harmless, for occasionally it enlarges andbecomes occupied by tumours, sometimes of large sizeand complex constitution, which cause death frommechanical interference with the brain. Darwin has pointed out that rudimentary (vestigial)parts are apt to be highly variable. This variabilityhe thought
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Keywords: ., bookcentury1800, bookdecade1890, booksub, common=tuatara, taxonomy
