maxillaries with teeth, hair, and skin, rudimentary bowel, gland, and brain traces), even in undoubted virgins, proves that even the human ovum is capable of parthenogenetic development. While such development, so far as known to science, is always abortive, and while, as Washington Irving remarks, the ingenious maiden who to-day would attribute conception to any other cause than sexual congress would find it difficult to overcome the prejudice of scientists, yet embryology, while declaring immaculate generation improbable, does not pronounce it impossible. A worker bee may be an offspring of an unimpregnated queen bee. What is a regular occurrence in one class of animals is sometimes observed as an exceptional one in another class. If the startling and apparently miraculous nature of a virgin generation of a living child be regarded as the sole objection to receiving such a fact, its defender might urge that the virgin generation of a dermoid cyst with all the traces, however aborted, of vertebrate organisation, is only a shade less startling and miraculous. This power of parthenogenesis, however, cannot continue indefinitely without extinction. This has been shown by the careful experiments of Maupas, who had observed 215 generations of an infusorian without sexual union. He found that then the family became extinct. Powers of nutrition, division, and conjugation with unrelated forms come to a standstill. The first symptom of this senile degeneration is decrease in size, which may go on till the individuals only measure a quarter of their normal proportions. Various internal structures then follow suit "until at last formless abortions occur, incapable of living and reproducing themselves." The nuclear changes are no less momentous. The important paranucleus is fatally sterile. The larger nucleus may also become affected, "the chromatin gradually disappears altogether." Physiologically, too, the organisms become manifestly weaker, though there is excessive sexual excitation. Such senile decay of the individuals and of the isolated family inevitably ends in death. Sexual union in those infusorians, dangerous perhaps for the individual life, a loss of time so far as immediate multiplication is concerned, is, in a new sense, necessary for the species. The life runs in cycles of a sexual division which are strictly limited. Conjugation with unrelated forms must occur else the whole life ebbs. Without it the protozoa, which some have called "immortal," die a natural death. Conjugation is the necessary condition of their eternal youth and immortality.