80 Rand and Boyden, lûequality of the two Eyes in regenerating Planarians. 



axis have a strong tendency toward the regeneration of eyes which 

 are temporarily unequal in size, one eye developing faster than the 

 other; secondly, that the positional relations of the larger and 

 smaller eye are closely correlated with the form of the regenerating 

 piece, which depends upon the nature of the operations to which 

 the worm has been subjected. In stating, as we have often done, 

 that the "outside" eye is larger than the other, nothing is implied 

 as to what makes it larger. There is nothing in the mere fact of 

 its being outside, or in its relation to convexity and concavity of 

 axis which could make it grow faster than its fellow. The caases 

 of the unequal development of the eyes may conceivably lie amongst 

 such factors as relations to light, differences in the rate of meta- 

 bolism (perhaps correlated with differences in the degree of muscular 

 activity) on the two sides of the unsymmetrically injured hodj, or 

 differences in the kinds or quantity of tissue participating in the 

 regenerative growth on the two sides of the body. Or may it be 

 that the unequal differentiation of the two eyes is a necessar}^ con- 

 sequence of the distribution of developmental and regulatory energies 

 in an unsymmetrically injured animal whose organization is bilaterally 

 symmetrical? In a further paper the senior author will describe 

 some supplementary experiments and discuss the symmetry of 

 regenerating planarians. 



Bibliography. 



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