ADVENTITIOUS REPRODUCTION IN HARENACTIS. I I 



unchanged, whatever the positions of the visible granules. As 

 a matter of fact most, if not all eggs actually show a more or less 

 sharp localization along the polar axis of processes differing in 

 degree or kind : in general the region of the animal pole reacts 

 more rapidly in various ways than the vegetative pole and be- 

 tween these two poles a gradation apparently exists. In every 

 fragment of such eggs above a given size this gradation must 

 exist in some degree, i. e., such fragments will retain the original 

 polarity of the whole. If, however, we could control the size 

 of isolated egg fragments and if it were possible to reduce the 

 size of nucleated fragments indefinitely we should undoubtedly 

 find a limit below which polarity would no longer be apparent. 

 In every case w r here control of the size of isolated pieces is possible, 

 such a limit has been found : unfortunately the egg cell is exceed- 

 ingly unfavorable material for experiment along this line. It 

 is at present extremely difficult and often impossible to isolate 

 pieces of the egg of a certain desired size or from a certain desired 

 region: moreover, if the isolated fragment is to live and show 

 any developmental processes it must possess a nucleus. Mani- 

 festly the possibilities of investigating the polarity and symmetry 

 of the egg by means of isolated fragments are very narrowly 

 limited, as compared with the possibilities which simple organisms 

 with elongated axes present, and we have no right to draw con- 

 clusions as to the nature of polarity from experimentation on 

 eggs alone. Until we can actually prove that in eggs polarity 

 does not decrease with decrease in size below a certain limit, or 

 until we can demonstrate the orientation of particles or molecules 

 by means of the polariscope, we have no adequate grounds for 

 regarding polarity as anything but a molar phenomenon. More- 

 over, the fact already mentioned, that in all cases w y here control 

 of the size of the isolated piece is possible, and where extended 

 experimentation has been made, the phenomena of polarity do 

 decrease with decreasing size, should suggest the necessity of 

 caution in drawing conclusions from eggs alone, where both 

 technical and natural obstacles to exact experimentation along 

 these lines exist. Moreover, I fail to see how we can avoid 

 accepting the evidence which the polariscope gives as possessing 

 much greater weight than the results of experiment with our 



