THE CHROMOSOMES OF SEA URCHINS, ESPECIALLY ARBACIA PUNCTULATA; A METHOD FOR STUDYING UNSECTIONED EGGS AT FIRST CLEAVAGE

Abstract

A method has been developed to stain the chromosomes and nuclei of unsectioned sea urchin and sand dollar eggs during the early cleavage divisions. The chromosome number of Arbacia punctulata is 44, and a karyotype of the pre-metaphase chromosomes of the first cleavage division has been made. The chromosome number of Echinarachnius parma is 44-46 and no karyotype has as yet been made.