We must carefully distinguish the rarer cases of real hermaphrodism from the preceding. This is only found when the essential organs of reproduction, the genital glands of both kinds, are united in one individual. In these cases either an ovary is developed on the right and a testicle on the left (or vice versa); or else there are testicles and ovaries on both sides, some more and others less developed. As hermaphrodism was probably the original arrangement in all the Vertebrates, and the division of the sexes only followed by later differentiation of this, these curious cases offer no theoretical difficulty. But they are rarely found in man and the higher mammals. On the other hand, we constantly find the original hermaphrodism in some of the lower Vertebrates, such as the Myxinoides, many fishes of the perch-type (serranus), and some of the Amphibia (ringed snake, toad). In these cases the male often has a rudimentary ovary at the fore end of the testicle; and the female sometimes has a rudimentary, inactive testicle. In the carp also and some other fishes this is found occasionally. We have already seen how traces of the earlier hemaphrodism can be traced in the passages of the Amphibia. Man has faithfully preserved the main features of his stem-history in the ontogeny of his urinary and sexual organs. We can follow their development step by step in the human embryo in the same advancing gradation that is presented to us by the comparison of the urogenital organs in the Acrania, Cyclostomes; Fishes, Amphibia, Reptiles, and then (within the mammal series) in the Monotremes, Marsupials, and the various Placentals. All the peculiarities of urogenital structure that distinguish the mammals from the rest of the Vertebrates are found in man; and in all special structural features he resembles the apes, particularly the anthropoid apes. In proof of the fact that the special features of the mammals have been inherited by man, I will, in conclusion, point out the identical way in which the ova are formed in the ovary. In all the mammals the mature ova are contained in special capsules, which are known as the Graafian follicles, after their discoverer, Roger de Graaf (1677). They were formerly supposed to be the ova themselves; but Baer discovered the ova within the follicles (Chapter 1.3). Each follicle (Figure 2.407) consists of a round fibrous capsule (d), which contains fluid and is lined with several strata of cells (c). The layer is thickened like a knob at one point (b); this ovum-capsule encloses the ovum proper (a). The mammal ovary is originally a very simple oval body (Figure 2.387 g), formed only of connective tissue and blood-vessels, covered with a layer of cells, the ovarian epithelium or the female germ epithelium. From this germ epithelium strings of cells grow out into the connective tissue or "stroma" of the ovary (Figure 2.403 b). Some of the cells of these strings (or Pfluger's tubes) grow larger and become