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The Nature of Biological Diversity 



and left). Unlike doublets, however, these two oral segments were 

 not 180° apart. Instead, the two mouths were 90° or less apart and of 

 course there was much less separation between the left kinety fields 

 of the right segment and the right kinety fields of the left segment. 

 Further, the anterior and posterior sutures of the left oral segment 

 curved to the right instead of to the left, meeting the sutures of the 

 right oral segment at common poles. In many of these cells a third 

 cytopyge appeared between the two on the postoral sutures. The 



New type 

 (see Fig. 8) 



FIG. 7. Diagram of origin of the new type of animal shown in Fig. 8. A. Exposure 

 to antiserum of two singlets conjugating with a doublet., B. Only one singlet sepa- 

 rating, but with cytoplasmic bridge joining it to doublet. C. This singlet separated, 

 but bore a hump. The nick in the doublet indicates that the source of the hump 

 was a piece of cortex from doublet mate, t indicates death of doublet and other 

 singlet; tbese never separated. D. The singlet one day later: hump "assimilated" ; 

 posterior half of body enlarged. E. First fission. F. One of the two daughter cells 

 is a new cell type, note: It is not known whether the new type came from the 

 posterior or anterior product of this fission, only that one product produced a clone 

 of the new type and the other did not. 



