216 



CELLS, TISSUES, AND ORGANISMS 



the chick cells became organized into kidney tubules; the mouse cells 

 formed cartilage ( Figure 14 ) . In other words, cells of each type— and, 

 in this case, of each species— congregated separately into functional 

 groupings. Careful examination revealed no noticeable interconversion 

 of cells from one type into the other; in spite of the close intermingling, 

 the cells retained their original histogenetic identities and grouping 

 preferences ( Moscona, 1957a; Auerbach and Grobstein, 1958; see also 

 Scott, 1959). 



These results with rotation-compounded aggregates parallel com- 

 pletely those previously, obtained in self-aggregating systems, and they 

 may be considered as firmly supporting the thesis that motivated the 

 tests. In confirming the retention by cells— under the conditions em- 

 ployed—of pre-established developmental traits, they solidly support 

 the conclusions about selective sorting out and grouping of com- 

 pounded cells. They also disclose that the cellular activities and the 

 intercellular mechanisms involved in bringing about preferential group- 

 ing and regional assortment reflect the type-identities of cells more 

 closely than their generic affiliations. It might be pointed out here that 

 the interpretation of cellular grouping in terms of preferential, type- 

 specific interactions conforms well with data from studies on the dis- 

 tribution of cells injected into the organism ( Weiss and Andres, 1952 ) , 

 and particularly with the results of repopulation of radiation-injured 

 tissues (Billingham, 1959). The successful implantation of rat blood 

 cells in the bone marrow of irradiated mice ( Ford et at, 1956 ) suggests 

 that not only under conditions of culture but in the organism as well 

 the properties involved in selective grouping of cells may be effective 

 across generic distances. 



At this point a parenthetical note seems indicated regarding the 

 retention by dispersed and aggregated cells of their pre-dissociation 

 identities and prospective functions. The material dealt with here re- 

 lates to cells at stages of development at which their developmental 

 fate had presumably been stabilized. Therefore the possibiHty must 

 not be excluded that with cells from earlier stages different results 



Figure 14. Part of an aggre- 

 gate compounded of mouse 

 cartilage-forming cells and 

 chick mesonephros cells. Note 

 the grouping of cells from 

 each species according to 

 their histogenetic function. 



