vation necessarily survive, while the weak in resources must disappear from the scene. Hence those which survive must display some especial fitness for existence under the circumstances of their environment, whatever they may be. So the "survival of the fittest" is believed to be a law of evolution, and the process by which it is brought about has been termed "natural selection." The works of Darwin and others have satisfied biologists that this is a vera causa.

Before the excellence of a machine can be tested, it must exist, and before man or nature selects the best, there must be at least two to choose from as alternatives. Furthermore it is exceedingly improbable that the nicely adapted machinery of animals should have come into existence without the operation of causes leading directly to that end. The doctrines of "selection" and "survival" plainly do not reach the kernel of evolution, which is, as I have long since pointed out, the question of "the origin of the fittest." The omission of this problem from the discussion of evolution, is to leave Hamlet out of the play to which he has given the name. The law by which structures originate is one thing; those by which they are restricted, directed, or destroyed, is another thing.

There are two kinds of evolution, progressive and retrogressive; or, to use expressions more free from objection, by addition of parts, and by substraction of parts. It is further evident that that animal which adds something to its structure which its parents did not possess, has grown more than they; while that which does not attain to all the characteristics of its ancestors has grown less than they. To express the change in the growth-history which constitutes the beginning of evolution, I have employed the terms "acceleration and retardation." Generally these expressions are literally exact, i. e., there is an increased rate of growth in evolution by addition, and a decreased rate in evolution by subtraction; but this is not always the case, for some divisions of animals have increased the length of their growth-period without reference to evolution in structure. The terms express the phenomena figuratively, where not exact in the sense of time, and I believe they are sufficiently clear. The origin of the fittest is then a result of either acceleration or retardation. It is easy to perceive that a character which makes its appearance in a parent before or near to the breeding season is likely to be

transmitted to its descendants; so also a character which is lost near this time is likely to be wanting from the offspring. The causes of acceleration and retardation may next claim attention.

It is well known that the decomposition of the nutritive fluids within living animals gives rise, in the appropriate tissues, to exhibitions of different kinds of forces. These are, motion in all classes; heat in some only; in a still smaller number, electricity and light; in all, at certain times, growth-force or bathmism; in many, phrenism or mental or thought-force. These are all derived from equivalent amounts of chemical force which are liberated by the dissolution of protoplasm. This organic substance, consisting of CHON, undergoes retrograde metamorphosis, being resolved into the simpler CO2, HO, etc., and necessarily liberates force in the process. None of the functions of animal life can be maintained without supplies of protoplasm. We have here to do with bathmism. It consists of the movement of material to, and its deposition in, certain definite portions of the growing egg, or fœtus, as the case may be. It is different in its movements in every species, and its direction is probably the resultant of a number of opposing strains. In the simplest animals its polar equilibrium is little disturbed, for these creatures consist of nearly globular masses of cells. As we ascend the scale a greater and more marked interference becomes apparent; radiated animals display energy in a number of radiating lines rather than in the spaces between them; and in longitudinal animals, a longitudinal axis exceeds all others in extent and importance. In the highest animals its results are much more evident at one extremity of the axis (head) than at the other, and the diverging lines are reduced to four (the limbs). In each species the movements of this force are uniform and habitual, and it is evident that the habit is so deeply seated that only a very strong dynamic interference can modify or divert it. The interfering forces are probably all those transmissible through living tissue, and especially molar force. Thus every species has its own specific kind of bathmic force.

The characters of living beings are either adaptive or nonadaptive; they are either machines especially fitted to meet the peculiarities of their environment, or they are not. Among the latter may be ranged rudimental structures and also many others

of no sufficient use. They are all due either to excess or defect of growth force; they are either consequences of a removal of nutritive material to other portions of the body; or they are due to an excess of such material which renders an organ or part useless through disproportionate size. Of the former class may be cited the absence of the tail in some monkeys and birds; also of the teeth in some Cetaceans; of the latter kind are the enormous tusks of the mammoth and the recurved superior canines of the babyrussa. The change of destination of this material has been probably due to the construction of adaptive machines whose perfection from time to time has required the use of larger and larger proportions of force and material.

In considering the origin of adaptive structures, two alternative propositions are presented to us. Did the occasion for its use follow the appearance of the structure, or did the need for the structure precede its appearance? The following answer to the question has always been the most intelligible to me. Animals and plants are dependent for existence on their environment. It is an every-day experience that changes in environment occur without any preparation for them on the part of living things. If the changes are very great, death is the result. It is evident that the influence of environment is brought to bear on life as it is, or has been, and that special adaptations to it on their part must follow, not precede changes of climate, topography, population, etc. We have another important consideration to add to this one, viz: the well-known influence of use, i. e., motion, on nutrition. Exercise of an organ determines nutritive material to it, and the nervous or other influence which does this, equally determines nutritive material to localities in the body to which an effort to move is directed, whether an executive organ exist there or not. The habit of effort or use determining the nutritive habit must be inherited, and result in the growing young, in additional structure. Change of structure, denied to the adult on account of its fixity, will be realized in the growing or plastic condition of fœtal or infant life. The two considerations here brought forward lead me to think that the cause of acceleration, in many adaptive structures, is environment alone, or environment producing movements, which in turn modify structure. The character of the stimulus in the successive grades of life may be expressed by the following table, passing from the lowest to the highest:

I. Passive or motionless beings;

by climate and food only.

2. Movable beings;

by climate, food and motion. By motion either;

a, unconscious, or1

aa, conscious, which is,

b, reflex, or

bb, directed by desire without ratiocination, or bbb, by desire directed by reason.

The only general rules as to the direct influence of motion on structure which can be laid down at present are two, viz: That density of tissue is in direct ratio to pressure, up to a certain point; and that excess of growth force, in a limited space, produces complications of the surfaces stimulated. These and other laws, yet unknown, have probably led the changes expressed by evolution, while many others have followed the disturbance of equilibrium which they have produced.

I here allude incidentally to the question of transmission or inheritance. It has been maintained above that the bathmic force of each species is different from that of all other species. This force is characteristic of some unit of organization of living beings; and this probably consists of several molecules. This unit has been termed, by Haeckel, the plastidule. The transmission of the bathmic force of one generation to another would be effected by the transmission of one or more living plastidules; and this is probably precisely what is accomplished in reproduction. The Dynamic Theory of reproduction I proposed in 1871,* and it has been since adopted by Haeckel under the name of perigenesis. I compared the transmission of bathmic force to that of the phenomenon of combustion, which is a force conversion transmitted from substance to substance by contact. The recent observations of Hertwig, Bütschli and others, confirm this view. The theory of pangenesis, devised to explain thẻ phenomenon of reproduction, is to my mind quite inadequate.

1 Movements coming under this head are often called reflex.

2 See Penn Monthly, 1872.

3 Method of Creation," Philadelphia, 1871.

4" Method of Creation," 1871.

EXPLANATION OF CUTS OF CRANIA OF ANURA.

The numbers in each column correspond with the types of ossification mentioned in the text, and are the same as those in the table of families given in the same connection. The power numbers attached to Fig. 3, represent the degree of ossification of the nasal bones, except the −1, which signifies unossified ethmoid. Most of the cuts are original.

BufonidÆ.—Fig. 2, anterior part of skull of Chelydobatrachus gouldi Gray, from Australia. Fig. 3, do of Schismaderma carens Smith, S. Africa. Fig. 6, top of head of Peltaphryne peltacephala D. and B., Cuba. Fig. 7, top of head of Otaspis empusa Cope, Cuba.

SCAPHIOPIDE AND PELOBATIDE.-Fig. 2, diagram of top of cranium of Didocus calcaratus Micahelles, Spain. Fig. 5, skull of Scaphiopus holbrooki Harl., United States. Fig. 6, skull of Cultripes provincialis, from France, after Dugès. HYLIDE.-Fig. 1, Thoropa misiessi Bibr., Brazil. Fig, 2, Hypsiboas doumerci D. and B., Surinam. Fig. 21, Hypsiboas punctatus Schn., Brazil. Fig. 32, Scytopis venulosus Daudin, Brazil. Fig. 6, Trachycephalus geographicus D. and B., Brazil, after Steindachner. CYSTIGNATHIDE.-Fig. 1, Eusophus nebulosus Gir., Chili. Fig. 2, Borborocates tasmaniensis Gthr., Tasmania. Fig. 3, Elosia nasus Licht., Brazil. Fig. 33, Hylodes oxyrhynchus D. and B., W. Indies. Fig. 4, Grypiscus umbrinus Cope, Brazil. Fig. 6, Calyptocephalus gayi D. & B., Chili.

RANIDE.-Fig. 3', Ranula chrysoprasina Cope, Costa Rica. Fig. 3, Rana oxyrhyncha Sund., S. Africa. Fig. 31, Rana clamitans Daud., N. America. Fig. 32, Rana agilis Mus., Berol. Fig. 33, Rana hexadactyla Less., India. Fig. 4, Polypedates quadrilineatus D. and B., Ceylon.

THE

[To be Continued.]

:0:

CONCERNING AMBER.1

BY ERMINNIE A. SMITH.

HE history of amber illustrates most clearly not only the slow and tedious growth of civilization, but also the seeming perversity and obtuseness of human nature, which, especially in former times, so retarded the advancement of science. Exhuming this history from the dim, far distant, prehistoric past, we find that from being first used for fuel by the almost barbaric northern hordes, among the more refined southern peoples, amber, like bronzes and their other articles of luxury, took the place of coin and had its economical and financial import. The oldest written documents that have come to us, mention it as one of the chief articles of luxury of the ancient civilized world, an object of greater request than fine gold.

1 Read before the "American Asso. for the Advancement of Science," at Saratoga, August, 1879.