body have a common architecture, which is bequeathed from generation to generation by means of the sexual cells. The cells which combine into an organ have, besides that, a structure specific for the organ. We are bound to accept this view, otherwise it would be incomprehensible why, for instance, the cells of the liver should produce only bile, and the cells of the medulla of the suprarenal bodies adrenalin, &c. All the cells of the body have certain functions to perform which are of use to the whole organism. It is quite certain that the different organs supply substances to the blood, which set up definite processes in other particular parts of the organism. If these substances are to act effectively, they must have a definite specific structure. The cells, too, on which they are destined to act, must also be characterized by a special structure, otherwise it would be difficult to understand why a special secretion acts only upon certain cells, and leaves a number of other cells quite unaffected.
A particularly fine example of the specific action of gland secretions upon cells of specific structure is supplied by such cases of hermaphroditismus verus as that, for instance, in which the bullfinch is found to have a testicle on one side and an ovary on the other. These peculiar animals have on the one side male, and on the other female, plumage, each being delimited accurately, and without any transition, along the middle line of the body. It is absolutely
