MORPHOGENESIS 785 



function almost continuously (cf. Hartmann, 1928). Is there a minimal 

 protoplasmic mass of definite size within which the organization of the 

 species can find latent expression — i.e., what is the smallest fragment 

 capable of regeneration.'* 



After shaking Stent or into fragments, Lillie (1896) learned that the 

 smallest nucleated piece of S. polymorphus to become a perfect form was 

 equal to a sphere of approximately 80 |j in diameter. Since the average 

 diameter of the normal forms was 230 |j, the smallest piece was about 

 one twenty-seventh of the original. The same approximate proportions 

 were obtained for 5". coeruleus. For the latter species, Morgan (1901) 

 obtained minimum values which were even less than those of Lillie. 

 The smallest regenerates produced were one sixty-fourth of the volume 

 of large normal stentors. According to Morgan, the conclusion that a 

 piece one twenty-seventh or even one sixty-fourth of the entire animal 

 can produce a new individual gives only a general idea of the relative 

 size of the minimum reorganization volume. More depends upon the 

 size of the normal individual than on that of the smallest piece, for 

 normal size limits vary considerably; a large normal individual may 

 contain eight times the volume of a small normal cell. The absolute size 

 of the smallest fragment is of greater significance than its relative size. 



Sokoloff (1923, 1924) was mainly interested in the minimum volume 

 necessary for regeneration and the rate of regeneration in pieces cut from 

 different regions. For Spirostomum the minimum volume was between 

 one fifty-third and one sixty-ninth of the initial volume, and was not the 

 same for pieces taken from different regions. In general, he found dif- 

 ferent rates in pieces of dififerent sizes; within certain limits, the larger 

 the piece the greater the rate. A comparison of his results with four genera 

 is given in the accompanying table (Table 21). In a type like Spiro- 

 stomum, the substance of which is qualitatively different as regards ability 

 to regenerate, the minimum volume and rate of regeneration varied ac- 

 cording to the region from which it was taken. In other Infusoria 

 [Dileptus, Burs aria, and Frontonia) the substance of the body appeared 

 to be qualitatively similar throughout (Sokoloff, 1923). 



Moore (1924) obtained successful regenerates from Spathidium frag- 

 ments as small as 1.3 percent of the original volume. The minimum re- 

 organization mass in Chaos diffluens was determined to be one eightieth 

 of the normal volume (Phelps, 1926). 



The proportionality of the regenerated structures to the size of the 



