FUSION MASSES OF WHOLE STENTORS 213 



normal orientation (Tartar, 1957c) and, remarkably, the same 

 behavior is shown in operated early sea urchin embryos 

 (Horstadius, 1950). These shifts are as if like parts exert a strong 

 ** attraction " for each other, and their coming together is an 

 important step in the unification of a fusion mass. 



Selective resorption of parts occurs not only on the lateral stripes 

 but also within the joined heads. When two sets of feeding organelles 

 become tightly apposed, first those sections of the two membranellar 

 bands are resorbed which permit the formation of a single ring 

 and frontal field. Extra tails are resorbed or sloughed, or they may 

 lose their separate identities by fusion. In all these precise adjust- 

 ments between the parts of grafted cells we see the specific acts by 

 which wholeness is achieved. 



3. Larger masses and reduction of oral valency 



Grafts of 5 to 100 animals were necessarily of random orientation 

 and displayed several interesting emergent characteristics which 

 are shown in Fig. 61. 



Most obvious is that grafts of 6 or more animals cannot attain 

 the unitary shape and giant individualities are not achieved. 

 Instead, the general impression is that of bas reUef sculpturing, as 

 if each set of stripes were able to make an individual hump in the 

 over-all contour. Although Stentor is able to make perfect forms 

 in tiny fragments, it is apparently unable to cope with a mass much 

 larger than it would ever encounter in nature. This is not because 

 such masses are necrotic. Their limitations seem to be morpho- 

 genetic rather than physiological. Either they represent simply a 

 self-defeating jumble or the upper size limit to form development 

 and regulation bears in itself important theoretical implications. 

 Lillie's '' minimal organization mass " seems to have lost its 



E. Similar, showing integration accomplished by resorption 

 in only one membranellar band. Apparently, parts of the band 



are resorbed when they do not subtend lateral striping. 



F. Adjustment in a graft complex, showing how just those 

 portions of the membranellar bands are resorbed which make 



for an integrated frontal field. 



G. Product of graft of two stentors in early division. Acces- 

 sory tail-pole and holdfast move posteriorly but are eventually 



resorbed (x). 



