620 



SCIENCE. 



[N. S. Vol. I. No. 23. 



tion of the molecular mecliauism of the 

 germ, the nature of which is still quite un- 

 kuown to us. 



Equally remarkable are the phenomena of 

 heteromorphosis described by Loeb, whose 

 experiments prove that some animals, like 

 most vegetable organisms, maj- adjust the 

 molecular machinery of their organization 

 in any new direction whatever that may be 

 arbitrarily chosen, so as to realize the con- 

 tinuance by growth of the same morpho- 

 logical result as that which characterized 

 them normally. These experiments would 

 at first thought seem to prove that some 

 organisms were isotropic, but such a con- 

 clusion is exceedingly doubtful. It may be 

 that such organisms are, as molecular 

 mechanisms, when subjected to new geo- 

 tropic and heliotropic conditions, capable of 

 correspondingly new adjustment? of their 

 molecular mechanical structure. But this 

 would not be proof of isotropy — only proof 

 of the assumption of a new condition of 

 feolotropy, adjusted in respect to a new 

 axis of reference, that also coincides mth 

 some part of the earth's radius prolonged 

 into space. This readjustment of the mole- 

 cular mechanism may be effected in some 

 way by gravity, as Loeb himself has sus- 

 pected. It is certainly not due to the con- 

 trol of any lurking ' biophors,' since it is a 

 purely mechanical readjustment of an ultra- 

 microscopic structure to new conditions 

 which cannot be effected in any other than 

 a mechanical way. 



The production of monstrosities also may 

 be explained by a dynamical hj-pothesis, 

 provided we assume that the forces of 

 ontogeny must operate against the statical 

 equilibrium of the parts of the germ at 

 everj' step. Especially if we assume in ad- 

 dition, as is born out by facts, that the 

 feolotropy and consequent recapitulative 

 power of the germinal substance is most 

 marked in certain regions of the embryo. 

 These regions, if their molecular equilib- 



rium be mechanically or otherwise disturlied 

 by division during development, will assert 

 their germinal potentialitj' and produce an~ 

 embrj'o, the relations of which to that 

 ali'eady formed alongside of it will be modi- 

 fied by the statical conditions of surface- 

 tension afforded by the adjacent embryo or 

 the uuderlj'ing yoke, or by both combined. 

 This is beautifully illustrated bj- a host of 

 facts. Double toes must have so arisen, as 

 is proved by the direct experiments of 

 Barfurth, some of which I have repeated, 

 as well as by what happens when the toes 

 of an Axolotl are persistently nibbled off 

 by another animal, when duplication may 

 not only take place in the horizontal plane 

 of the foot or hand, but also in the vertical 

 one. In this way a number of supernum- 

 erary toes niaj' be caused to arise from a 

 single stump, provided the re-growth of the 

 toe be so interfered with as to compel 

 regeneration from two terminal re- 

 genei'ative surfaces instead of one. This 

 must follow from the law demonstrated by 

 Barfurth's experiments, namely, that the 

 regeneration of an organ tends to occur uni- 

 formly over and in a direction normal to 

 the regenerating surface. In this way it is 

 possible to mechanically determine the di- 

 rection in which a regenerated part shall be 

 reproduced by merely making changes in 

 the angular relations of the plane of the re- 

 generating surface to that of the axis of the 

 body, as indicated by the diagram in Fig. 2 

 of the regenerated tail of a tadpole. Here 



the line I indicates the plane along which 

 the tail has been removed, ii2)0u which re- 

 generation will restore the tail straight 



