advantageous organic variations die with the individual, and must be born again, so to speak, with each new individual." This requires time, and progress depending on it would be indefinitely protracted. On the other hand, by means of social heredity, each new member of the race has handed to him at birth the accumulated organic advantageous variations of sense and motor organs, and the extra-organic adaptations that have multiplied so indefinitely in the age of civilized man. "The vast importance of accumulation of capital is obvious." =Fossils as criterions of Geological Ages.=--Prof. O. C. Marsh said in a paper on The Comparative Value of Different Kinds of Fossils in determining Geological Age, which was read at the meeting of the British Association, that the value of all fossils as evidence of geological age depends mainly upon their degree of specialization. In invertebrates, for example, a lingula from the Cambrian has reached a definite point of development from some earlier ancestor. One from the Silurian or Devonian, or even a later formation, shows, however, little advance. Even recent forms of the same or an allied genus have no distinctive characters sufficiently important to mark geological horizons. With ammonites the case is entirely different. From the earliest appearance of the family the members were constantly changing. The trilobites show a group of invertebrates ever subject to modification, from the earliest known forms in the Cambrian to the last survivors in the Permian. They are thus especially fitted to aid the geologist, as each has distinctive features and an abiding place of its own in geological time. In the fresh-water forms of mollusca--the Unios, for example--there is little evidence of change from the palæozoic forms to those still living, and we can therefore expect little assistance from them in noticing the succeeding periods during their life history. The same law as to specialization holds good among the fossil vertebrates.