Chromosomes of artificially activated eggs of Urechis

The eggs of Urechis that cleave and develop as a result of activation by dilute sea water have been previously shown (Tyler, 1931a) to be those which extrude no polar bodies. It would appear then that the embryos produced by such eggs might be tetraploid, diploid, or haploid, depending upon the behaviour of the chromosomes during the first two nuclear divisions. A cytological investigation of such eggs shows. that the embryos are diploid in chromosome number, and that only one maturation division occurs. The preparations were made by a method used by Karl BélaFand similar to that described by him (1928). It consists of joining and later Separating two cover-slips, one containing a drop of eggs and the other a drop of fixing fluid. The eggs are flattened to any desired extent and stick to the cover-slips, which can be handled in the same manner as slides containing sectioned material. Two types of eggs are produced as a result of activation with dilat