RECONSTITUTIONAL PATTERNS IN EXPERIMENT 419 



surface in contact and free surface as a center, and the osculum forms in 

 this region on the free surface. Gravity is not concerned; probably the 

 contact-free-surface oxygen differential is the chief factor, but demonstra- 

 tion seems to be lacking. Swimming sponge larvae in certain developmen- 

 tal stages aggregate when brought into contact, and sponges may de- 

 velop from the aggregates with osculum on the free surface and a pattern 

 without any conceivable relation to the pattern of individual larvae 

 (H. V. Wilson, 1907). 



Experiments with Corymorpha aggregates, consisting of cells from many 

 individuals, indicate that the contact-free-surface differential is the chief 

 factor in determining the polarity of the resulting individual or partial 

 form. Aggregates remaining undisturbed with one region continuously in 

 contact usually (79 per cent in characteristic lots) give rise to unipolar 

 complete individuals on a small scale of organization. Aggregates of ap- 

 proximately the same size, moved about and turned over repeatedly at 

 somewhat irregular intervals of one to several hours, usually (86 per 

 cent) develop only apical parts of the manubrium on a larger scale but 

 are mostly unipolar. Probably polarity is determined by the chfferential 

 exposure in intervals between change of position. Experimental attempts 

 to determine the time necessary for determination of polarity by the con- 

 tact-free-surface differential have not yet been performed, but it is cer- 

 tainly not long. In the aggregates moved about at intervals the changes 

 in position permit development on a much larger scale of organization; 

 consequently, apical partial forms are the characteristic result (Child, 

 1928c). Aggregates kept free from continued contact by water currents 

 or by continued change of position with respect to gravity by slow revolu- 

 tion on a vertical wheel in closed containers usually remain spherical, do 

 not develop at all, and finally, after several days, become completely in- 

 closed in perisarcal secretion and remain without further change, except 

 decrease in size of the living tissue inside the perisarc, until death. How- 

 ever, some aggregates develop partial or complete axes, even when kept 

 entirely free from continued contact on the revolving wheel, probably 

 because of the presence in some region or regions of the aggregate of a 

 higher level of cell activity, perhaps a few cells from distal stem-levels. 

 A few such cells near together by chance may initiate a new dominance 

 and gradient, and, if more than one such group is present, more than one 

 axis may develop. At present there is no evidence of determination of the 

 polarity of an aggregate by an inherent persistent polarity of its cells and 

 their orientation to each other. 



