body, as remarkable appendages above and below the
thalamencephalon. Their function, if they have a function, is altogether
unknown. Probably, they are inherited from ancestors to whom they
were of value. Such structures are called reduced or vestigial
structures, and among other instances are the clavicles of the rabbit,
the hair on human limbs, the little pulpy nodule in the corner of the
human eye, representing the rabbit's third eyelid, and the caudal
vertebrae at the end of the human spinal column. In certain lowly
reptiles, in the lampreys, and especially in a peculiar New Zealand
lizard, the pineal gland has the most convincing resemblance to an
eye, both in its general build and in the microscopic structure of its
elements; and it seems now more than probable that this little
vascular pimple in our brains is a relic of a third and median eye
possessed by ancestral vertebrata. The pituitary body is probably
equivalent to a ciliated pit we shall describe in the lacelet
(Amphioxus).
8. _Renal and Reproductive Organs_