ON THE EARLY DEVELOPMENT—BIPOLAR DIFFERENTIATION AND CLEAVAGE—OF THE ZEBRA FISH, BRACHYDANIO RERIO

Abstract

The egg of the zebra fish is an extraordinarily satisfactory laboratory object; it can be obtained every day of the yr., it is transparent and develops in about 60 hrs. from fertilization to hatching at 27[degree]C. For observation and measurements a moving picture was used, taken by time accelerator. 3 stages of bipolar differentiation were observed. The last one was immediately correlated with the changes in the physical state of the cells connected with mitosis. Not only the polar axis, but also the axis of the first cleavage plane was discernible 1 minute after fertilization. 1/2 hr. before the cleavage plane itself became visible.