78 FRANK R. LILLIE. 



The principle laid down here as to the molecular basis of cyto- 

 plasmic organization must apply not only to the stages considered 

 but to all stages of development and to all parts of the organism. 



The polarity of the egg and of living parts generally has been 

 compared to magnetic polarity. Thus parts of a magnet exhibit 

 polarity in the same direction as the original whole, and the north 

 pole of the part is as true a north pole as the north pole of the 

 whole magnet ; the same is generally true of polarity in living 

 things : a piece of Hydra, for instance, exhibits the same polarity 

 as the entire animal of which it is a part. But push the compari- 

 son a little farther and the analogy appears to break down : a 

 piece from the north end of a magnet has no more northness, so 

 to speak, than a piece of the same size from the south end ; on 

 the other hand, an animal piece of an entire egg or an oral 

 piece of an entire animal frequently has considerably more animal 

 or oral properties than a piece from the vegetative or aboral 

 end. The same difficulty of course arises if we use the analogy 

 of crystallization. But it may be that it is due to secondary 

 causes that modify the result without detriment to the validity 

 of either analogy. 



In conclusion a few words with reference to the so-called for- 

 mative stuffs : So far as they are to be identified with the visible 

 substances segregated by the centrifuge, it would appear to be 

 indicated by the experiments that they can play no specific role 

 in differentiation, because in centrifuged eggs they may occupy 

 variable positions in the embryo. I believe, however, that the 

 matter requires further investigation. It seems hardly credible 

 that the strictly determinate distribution of these substances in 

 normal ontogeny is meaningless, and that abnormal distribution 

 is a matter of indifference. It is noteworthy that a large propor- 

 tion of centrifuged eggs die before development has proceeded far, 

 and that there is a distinct tendency towards abnormalities in the 

 surviving eggs. It is natural to correlate these facts with unregu- 

 lated abnormalities of distribution of granular materials. In any 

 event a more careful study of the facts is needed. 



It should be borne in mind that only the factors of polarity 

 and bilaterality, the localizing factors in general, are shown to be 

 functions of the ground substance. The respective roles of 



