Their anxiety in this direction led them to consider the whole group of organs constituting a most important regulatory and coördinative system in man and other vertebrates as so many useless vestigial organs. This system is called the _cryptorhetic system_ and is made of internally-secreting, ductless glands, now called _endocrine glands_. These glands generate and instill into the blood stream certain chemical substances called _hormones_, which, diffusing in the blood, produce immediate stimulatory, and remote metabolic effects on special organs distant from the endocrine gland, in which the particular hormone is elaborated. As examples of such endocrine glands, we may mention the pineal gland (epiphysis), the pituitary body (hypophysis), the thyroid glands, the parathyroids, the islelets of Langerhans, the adrenal bodies (suprarenal capsules), and the interstitial cells of the gonads. The importance of these alleged useless organs is now known to be paramount. Death, for instance, will immediately ensue in man and other animals, upon extirpation of the adrenal bodies. The late Robert Wiedersheim, it will be remembered, declared the pineal gland or epiphysis to be the surviving vestige of a “third eye” inherited from a former ancestor, in whom it opened between the parietal bones of the skull, like the median or _pineal eye_ of certain lizards, the socket of which is the parietal foramen formed in the interparietal suture. If the argument is based on homology alone, then the coincidence in position between the human epiphysis and the median optic nerve of the lizards in question has the ordinary force of the evolutionary argument from homology. But when one attempts to reduce the epiphysis to the status of a useless vestigial rudiment, he is in open conflict with facts; for the pineal body is, in reality, an endocrine gland generating and dispersing a hormone, which is very important for the regulation of growth in general and of sexual development in particular. Hence this tiny organ in the diencephalic roof, no larger than a grain of wheat, is not a functionless rudiment, but an important functioning organ of the cryptorhetic system. We have no ground, therefore, on this score for inferring that our pineal gland functioned in former ancestors as a median eye comparable to that of the cyclops Polyphemus of Homeric fame.