A CYTOLOGICAL STUDY OF ARTIFICIAL PARTHE- 

 NOGENESIS IN CUMINGIA 



MARGARET MORRIS 

 Osborn Zoological Laboratory, Yale University 



FOUR TEXT FIGURES AND EIGHT PLATES 



I. INTRODUCTION 



The following experiments with the egg of the mollusc Cu- 

 mingia tellinoides were begun at Woods Hole in the summer of 

 1914. At first it was intended simply to find an easy method of 

 inducing artificial parthenogenesis and to make a cytological 

 study of eggs undergoing such development, A method was 

 soon found which gave a fair percentage of cleavage and a few 

 swimming larvae in most experiments. Early in the course of 

 the experiments, however, it was observed that while some eggs 

 gave off both polar bodies in the normal manner, others formed 

 only one, and still others passed at once to a 2-cell stage with- 

 out forming polar bodies at all. From the cytological study 

 made in the following winter, it was found that in some of the 

 eggs subjected to the treatment, both nuclei formed by the 

 division of chromosomes in the first polar spindle are retained 

 in the egg, and that these two nuclei fuse. It seemed as if a 

 sort of self-fertilization had taken place in these eggs, and the 

 question whether this process was the beginning of normal de- 

 velopment became the central one of the problem. The later 

 experiments were, therefore, made for the purpose of finding 

 out whether the swimming larvae obtained by the partheno- 

 genetic treatment came from eggs which had formed polar 

 bodies or from those which had not. When it was found that 

 normal larvae do, in fact, come from eggs in which maturation 

 has been suppressed, it was still necessary to determine from a 

 further study of preserved material whether the eggs in which 

 the polar nucleus fused with the egg nucleus were those which 



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THE JOURNAL OF EXPERIMENTAL, ZOOLOGY, VOL. 22, NO. 1 

 JANUARY, 1917 



