ATTEMPTS TO CULTURE ISOLATED URODELAN BLASTOMERES THAT CONTINUE TO DIVIDE WITHOUT AGGREGATING*

The blastomeres isolated from urodelan blastulae continued to divide without aggregating of daughter cells when inoculated with Ca²⁺-free neutral Holtfreter solution into glass culture dishes coated with agar. When standard Holtfreter solution with pH 8.2 was used as a culture medium, Ca²⁺ content from 1/40 to 1/20 of the original strength was essential for the purpose of the present observations; other divalent cations such as Mg²⁺, Ba²⁺ or Mn²⁺ replaced Ca²⁺. Under these experimental conditions, cell pedigrees were obtained during the incubation period. The greatest number of cell divisions so far observed in vitro was 8 for Hynobius lichenatus, and 9 for Cynops pyrrhogaster. Some related observations on the behavior of isolated blastomeres are also presented.