VEGETALIZATION OF PRESUMPTIVE ECTODERM OF NEWT GASTRULAE IN A TRANSFILTER EXPERIMENT WITH FISH SWIMBLADDER AS THE INDUCTOR.

The diffusibility of the vegetalizing factor was examined by a transfilter culture using an ethanol-fixed swimbladder of the crucian carp (Carassius auratus) as the inductor and presumptive ectoderm from gastrulae of Cynops pyrrhogaster as the responding tissue. Nucleopore filters, about 12-14 μm thick, with nominal pore sizes of 0.05, 0.1, 0.6, 0.8, 3.0 and 8.0 μm were interposed between the interacting tissues. The responding pieces of ectoderm were removed from the assemblies after contact for 0.5, 1, 3, or 24 hr and cultured in Holtfreter's solution for 10 days at 20°C. The inductions observed were almost entirely mesodermal, although masses of endoderm-like yolky cells were seen in explants and neural tissues in a few cases. Filter membranes with pores of 0.05 to 8.0 μm did not interfere with the vegetalizing effect. Under an electron microscope, small cytoplasmic cones of the responding cells of the presumptive ectoderm were observed in the pores of the interposed filter after 3 hr's contact. The cones grew longer as the cultivation time increased, but even after 24 hr there was no contact between the interacting tissues. Since 3 hr's contact between the interacting tissues was sufficient to cause full vegetalization on the transfilter culture with the swimbladder, the formation of the cytoplasmic outgrowths had no significance in the induction.