RECONSTITUTIONAL PATTERNS IN EXPERIMENT 395 



on each other are perhaps of interest. These effects have been pointed 

 out by various authors in attempts at analysis of the mitotic figure. For 

 example, if two like magnetic poles are brought near together, the field 

 of each is altered so that the two become mirror images of each other. If, 

 then, a third like pole is brought near on one side, so that it acts equally 

 on both fields, both acquire, so to speak, a dorsiventrality but are still 

 mirror images of each other. Similarly, two equal fields of fluid, each 

 flowing radially from a center, when near together alter each other so that 

 each becomes a mirror image of the other. A current flowing at right 

 angles to the line joining the two centers will determine a new asymmetry 

 in both fields, but they wifl still be mirror images. In both the magnetic 

 and the fluid fields a morphological asymmetry and mirror-imaging is es- 

 tabhshed and persists as long as the dynamic factors act; or if the mag- 

 netic field is made visible by iron particles, the pattern may persist after 

 removal of the poles. These examples of field action and resulting pattern 

 are offered merely as suggestions, not as models. 



Apparently reversal of asymmetry in one limb primordium by another 

 may depend on relative positions of the two. With transplantation in 

 certain orientations to a position anterior to the host limb bud, the asym- 

 metry of the transplant is reversed; with transplantation in normal orien- 

 tation posterior to the host limb bud, asymmetry of the host limb is re- 

 versed. In these combinations the posterior member always develops more 

 rapidly and the anterior member is reversed, apparently by the domi- 

 nance of the other (Takaya, 1936). These experiments suggest that posi- 

 tion in the anteroposterior body gradient may influence rate of develop- 

 ment and that developmental activity, rather than a structural pattern, 

 is the essential factor in influence of one hmb bud on another. In this 

 connection mirror-imaging of sea-urchin larvae developing from blasto- 

 meres of the two-cell stage in contact after separation (Driesch, 1906) 

 and the cases of situs inversus and mirror-imaging in twinning and double 

 monsters are of interest, as probably involving much the same factors as 

 amphibian limbs. In hydroid reconstitutions two hydranths developing 

 close together often show more or less inhibition on the facing sides and 

 so are mirror images. 



REGENERATION OF THE LENS IN AMPHIBIA 



The regeneration of the lens from the dorsal region of the iris in various 

 amphibia has presented a problem of considerable interest which has led 



