64 TitaJiiy and Organization of Protoplasm. 



ical fragment. And this is also found to be capable of reintegrating 

 in its own way the structure and form of the embryo as a whole. The 

 new fragment possesses no longer the same organic arrangement of the 

 egg-plasm as a whole; but, being of a lower chemical order, it takes up 

 the work of reintegrating the embryo at a less differentiated stage of its 

 structural reconstitution than had been the case with the normal egg- 

 plasm. • 



This hypothetical interpretation, unlike the fanciful conception of 

 aggregational and mechanical views^ flows consistently from the ascer- 

 tained nature of the living substance, as explained in the former section. 

 It is confirmed by the different stages of chemical or structural develop- 

 ment found established in the egg-plasm of different organisms. In 

 some organisms their egg-plasm consists of a less disintegrated or rather 

 higher integrated fragment than in others, and represents therefore a 

 more advanced and firmer stage of structural development or "matura- 

 tion," evincing itself in a more definitely and solidly differentiated or- 

 ganization, or so-called mosaic-like arrangement. 



The interpretation here ventured of these striking and most instruc- 

 tive ontogenetic phenomena, revealed by means of experiments with 

 egg-plasms, is signally corroborated by Morgan's experiment with the 

 substance of the living half blastomere of the egg of frogs, whose ad- 

 joining partner had been killed. Left in its normal position the living 

 blastomere developed into a half-embryo. By disturbing the "mole- 

 cular" or structural arrangement of its substance through reversion of 

 the egg, it developed an entire embryo of reduced size. Here the blas- 

 tomere possesses obviously at first a definite unilateral organization, de- 

 rived from the bilateral organization of the egg-plasm as a whole. Its 

 definite chemical constitution, representing only one-half of a normally 

 established ontogenetic germ, being upset, its living substance becoming 

 thereby further disintegrated, retains nevertheless its character of being 

 a fragment of the entire organism of which it is derived, and reinte- 

 grates itself as such, not to a half, but to an entire embryo. It forms 

 a new germ at a lower chemical level, involving potentially complete 

 formative potency. Even small artificially severed portions of egg- 

 plasm, at different stages of its ontogenetic evolution, retain the power 

 of reproducing not the mere structure of the plasm from which they 

 were immediately severed, but the structure and form of the entire em- 

 bryo; and their living substance must therefore reconstitute itself a 

 chemical fragment of the entire organism, of which it then proves to 

 be a reproductive germ. 



In a general way it may be asserted, that the higher the stage of chem- 

 ical integration, or ontogenetic evolution the egg-plasm represents in 

 relation to the whole embryo it is destined to reproduce, and also the 

 higher the organism of which it is derived stands in the scale of animal 

 development, the less readily will fragments of such egg-plasm, or frag- 

 ments of such organisms reconstitute themselves into totipotent germs. 

 In order t]]at fragments may become totipotent, their living substance 



