March. 1894. SOME NEW BOOKS. 21 s 



A Theory of Development and Heredity. By Henry B. Orr, Ph.D., Professor 

 at the Tulane University of Louisiana. New York and London : Macmillan 

 and Co., 1893. Price 6s. 



At the present time all theories of Development and Heredity are 

 classified naturally in accordance with the views of the writers about 

 the inheritance of acquired characters. Professor Orr accepts the 

 principle of such inheritance but he is somewhat cavalier in his 

 treatment of the question. He compares one-celled animals with 

 many-celled animals from the " physiological " point of view, and 

 comes to the conclusion that there is no sure foundation for the 

 assumption of a physiological difference between the great groups. 

 In the one case the mass of protoplasm is continuous : in the other 

 the protoplasm is intersected by cell-walls, running in all directions. 

 " In the simpler forms of the metazoa each cell has a nucleus : in 

 the more complex of the protozoa a single-celled animal may have 

 several nuclei. Thus we see that the nucleus affords no basis for the 

 assumption of such a profound distinction between the groups." 

 Cell-walls (primarily, at least) are merely "an indispensable means 

 of support." " None can maintain that the sluggish Hydra is a more 

 highly-developed organism than the graceful Stentor or Paramoecium." 

 In higher animals the complicated nerve-tracts place the organs in a 

 more immediate connection with each other even than the protoplasm 

 in the cells of Hydra. It is true, he admits, that metazoa differ from 

 protozoa in that they have germ-cells. But these are merely part of 

 the protoplasm which retains its original qualities, " only changing its 

 nervous condition to a condition of greater complexity of co-ordi- 

 nations." The germ-cells are, therefore, able to develop as did 

 their forbears, with the addition of the "nervous " changes impressed 

 on them by the forces of the environment. Professor Orr gives 

 instances showing that the germ-cells are not isolated from the rest 

 of the organism ; mstances like the effects on the body of castration ; 

 instances like changes of season determining the period of maturation. 

 But hear the Professor : — 



" Finally, since the germ-cells possess the potentiality of pro- 

 ducing all the nervous and mental traits of the body from which they 

 are derived, we cannot suppose them utterly disconnected from the 

 nervous system and inaccessible to its influence. There seems to be 

 a most profound and intricate connection between the two. 



" We find, therefore, no essential difference between the develop- 

 ment and reproduction of the protozoa and the same process among 

 the metazoa. If inheritance of acquired characters be admitted for 

 unicellular organisms (and I can see no other reasonable interpre- 

 tation of the fact), then the same must be admitted for multicellular 

 organisms." 



Biology, according to the Professor, stands between the science 

 of physics and psychology, and the laws of these cannot be 

 neglected in biological research. The forces of growth and develop- 

 ment must be regarded as transformations of the general sum of energy. 

 Starting from this he builds up a theory that is epigenetic in the ex- 

 tremest form. It is the pressure of the outer world that moulds and 

 forms the growing organism. Light and heat, vibrations and impacts, 

 the chemical and physical nature of gases and food-substances, are the 

 active forces at work, and by them protoplasm becomes organism. 

 Some examples will show the extent to which Professor Orr attributes 

 direct mechanical effect to the environment. The fauna of the Gulf 

 Stream are all yellow because the seaweed in which the animals live 

 is yellow, and living matter is capable of photographing colours : so 



