have nothing to do with the simple egg cell. Even in the case of other animals we often find large eggs with thick coverings. For example, the shark's; but even in this case the egg is originally exactly similar to those of mammals when in its primitive condition as it comes from the ovary. In the case of the bird these additions serve only as food for the growing embryo, which, in the case of mammals, is furnished by a stream of the mother's blood, making 'stored-up' nutriment unnecessary." Before, however, we can have _true germ plasm_ the mother cell must be fertilized by the male cell. This is true of all the higher plants and animals. There are some low plants and animals in which fertilization by the male cell is not required. This has been called virginal generation. In no mammal is this possible. How fertilization takes place and what it signifies are both important questions which have not been entirely settled, and it almost seems as if they could not be settled in some of their details, except in the lower forms of life. Nature has so protected the process from observation in the higher animals that it cannot be studied in detail; but in plants and the lowest animals it has been observed with some success, and we may infer that the process is very much the same in the higher animals. Haeckel, in his great work on the Evolution of Man, tells us that "The process of fertilization in sexual generation depends essentially on the fact that two dissimilar cells meet and blend. In former times the strangest views prevailed with regard to this act. Men have always been disposed to regard it as thoroughly mystical, and the most widely different hypotheses have been framed to account for it. It is only within a few years that closer study has shown that the whole process of fertilization is extremely simple, and entirely without special mystery. Essentially, it consists merely in the fact that the male sperm-cell coalesces with the female egg-cell. Owing to its sinuous movements, the very mobile sperm-cell finds its way to the female egg-cell, penetrates the membrane of the latter by a perforating motion, and coalesces with its cell material.