628 



H. MOSER, [. HADJI-AZIMI AND S. SLATKINE 



48 hours after explantation. Actively proliferating cells are predominantly of the 

 epthelioid varieties. Within an incubation period ranging from 2 to 3 weeks 

 the undifferentiated and actively proliferating cells form large dense sheets of 

 epithelioid cells (see Figure 5) or usually less dense sheets of fibrocyte-like cells 

 (see Figure 6). Many éléments in thèse highly heterogeneous primary cultures 



Fig. 4 a 



Primary-explant culture derived from 

 whole young Xenopus laevis tadpoles 

 (stages 42 to 45), grown for 2 weeks at 

 room température in TCM-A2. Fixed 

 (Bouin) and stained (Hematoxylin-eosin). 

 a) Section of the axial structure of the 

 tail with expanding epithelioid-cell sheet 

 (magnification, 148 X). 



Fig. 4 b 



b ) Section of the intestinal tract (magni- 

 fication, 160 X). 



undergo active differentiation. Melanoblasts and early stages of pigmented cells 

 (see Figure 7a) develop into fully differentiated melanophores (see Figure 7b, c). 

 A particular cell variety in the explant yields giant uni-nucleated cells whose 

 highly transparent cytoplasm contains many large fibrilles (see figure 8). Other 

 already differentiated éléments in the explant, such as for example notochord 

 tissue, retain their structural integrity for long periods of time, sometimes for 

 more than three weeks at room température. 



