EXPERIMENTS ON THE DEVELOPMENT OF EGG 

 FRAGMENTS IN CEREBRATULUS. 1 



N. YATSU. 



The question, "To what extent can the principle of germinal 

 localization be applied to the unsegmented egg, and how far, on 

 the other hand, may the specification of the embryonic regions be 

 considered a progressive process that falls under the category of 

 epigenetic phenomena?" (Wilson, 1903'") led me in the summer 

 of 1903 to carry out a series of removal-experiments on the eggs 

 of Cerebratulus lacteus, during the later part of my stay at the 

 Tufts College Marine Laboratory at Harpswell, Me. I wished 

 to determine whether the cytoplasmic localization is progressively 

 established, and especially to ascertain the conditions existing in 

 the egg just prior to the first cleavage. To this end I have 

 examined the development of egg fragments, obtained by cutting, 

 at four successive periods between discharge of the egg and the 

 first cleavage, namely, (i) before the dissolution of the germinal 

 vesicle, (2) at the metaphase of the first polar mitosis, (3) at the 

 period of conjugation of the egg- and sperm-nuclei and (4) after 

 the constriction of the first cleavage appeared. The result shows 

 that the percentage of abnormal larvae steadily increases as the 

 egg approaches the two-cell stage. When I appreciated the im- 

 portance of comparing with these results the development ot 

 isolated blastomeres of the two-cell stage, the breeding season was 

 nearly over, and I was only able to make a few experiments, 

 which are not numerous enough to give a satisfactory basis of 

 comparison. I hope, however, to carry on more complete ex- 

 periments at the first opportunity. 



A word about cutting the eggs. A drop of water containing 

 several eggs was spread on a slide, and some of the water was 



1 For the preparation of the present paper my best thanks are due to Professor E. 

 B. Wilson for his kindly suggestions and criticisms. I am also indebted to Professor 

 J. S. Kingsley for kindness shown me at the Harpswell Laboratory. 



2 E. B. Wilson, "Experiments on Cleavage and Localization in the Nemertine 

 Egg," Arch. f. Ent-w/n., Bd. 16, Heft 3, p. 440. 



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