MODERN PHILOSOPHICAL BIOLOGY. 721 



principle. Sound philosophy should discredit all such fanciful ideas. 

 The tendency merely signifies that these polarities, being complexeg 

 of the physiological units, can find equilibrium only in the form of the 

 adult organism to which they belong. To this equilibrium they tend, 

 not only by an internal impulsion, but also under the combined action 

 of external forces : the latter represent the force which arranges the 

 units in a new order, and the former the direction in which this 

 force is exerted. Now, the cells which go to reproduce an organ- 

 ism are in a state of unstable equilibrium and of minimum heteroge- 

 neity : but they are not indiiferent substances ; they are the vehiclee 

 of physiological units derived from the parents, and they follow only 

 the tendency impi-essed upon them by their polarities. The same is 

 to be said of the elements of the plasma from wliich a tissue or an 

 organ is reproduced. Thus we see that the resemblance of an organ- 

 ism to the organisms from which it is sprung is the result of the ten- 

 dencies proper to the physiological units which have come from the 

 parents. 



In the fecundated germ there are two groups of physiological 

 units, presenting in their structures slight differences, so that by their 

 fundamental resemblance they conspire to form an organism of the 

 species to which the parents belong, and by their diflferences they 

 give to this organism traits peculiar to each of the two parents. In this 

 way, simultaneously with transmission of generic and specific char- 

 acters, we have transmission of those which are peculiar to the indi- 

 vidual. Further, we see that characters due to variations called acci- 

 dental or spontaneous, because we are unable to assign their true 

 cause, must also be transmitted as a tendency of the physiological 

 units, provided this character has gained in the individual such a de- 

 gree of stability as henceforth to find its place in that individual's 

 state of equilibrium. The action of the surrounding conditions will 

 determine whether l^e tendency of the physiological units is to be 

 realized or frustrated. The tendency of the physiological units ex- 

 presses an internal equilibrium, and hence heredity is a consequence 

 of our first principles. 



One character of living things is the faculty of reproducing them- 

 selves, i. e., of emitting parts of themselves which develop into perfect 

 individuals. This property, in all respects analogous to that which re- 

 produces tissues, differs from the latter only as regards the production 

 of new individuals, or only parts of the same individual. There is an 

 analogy between the operation of generation and that of repair, but 

 there is also a difference. In repair the new pi'oducts are aggregated 

 around the same axis as the old, whereas in generation the new 

 product soon becomes itself the axis around which the increments 

 of nutrition group themselves. In reality, the contrasts are in excess 

 of the analogies ; generation is at bottom an operation of disintegra- 

 tion. This is very well seen in those low oi-ganisms which produce 

 yor,. VIII. 46 



