562 VEKA DANCHAKOFF 



organ, which disappeared after it had fulfilled its function during 

 cell division. 



Such controversies seemed to depend largely upon the general 

 view, that the cell organs are independent formations, equal in 

 all living cells. The principle of evolution, either phylogenetic 

 or ontogenetic, was not applied to the organs of the cell. Any 

 observation concerning the cell organs of different animals and 

 of different stages of development had to strictly correspond to 

 definite formula. Data, different only because they belonged 

 to various periods and different classes of animals, were regarded 

 as wrong and were rejected as not fitting into the artificially 

 created rigid limits of fixed theories. The principle of evolu- 

 tion of different classes of animals and the principle of evolution 

 of different stages of organ development, both aspects of the 

 same law, do not constitute the whole content of the law. The 

 principle of evolution appears as a most general quality of living 

 matter, and no tissue, no cell, no cell organ, can escape its oper- 

 tion. The different numbers in chromosome complexes of dif- 

 ferent animals and the different aspects of mitotic figures in differ- 

 ent tissues of the same animal may serve as an example. 



In my former studies on the develoi)ment of blood in birds 

 and reptiles, the ontogenetic development of a definite kind of 

 blood cells and their organs was repeatedly taken into consider- 

 ation. The small size of the blood cells, however, prevented a 

 more detailed study of the ontogenetic development of cell 

 organs. The study of the beautiful, transparent eggs of Stron- 

 gylocentrotus lividus seemed to offer an opportunity of verifying 

 some conclusions drawn from the study of differentiation of 

 blood cells. Some new facts observed in the development of 

 the eggs may help to correlate our conception of different mor- 

 phological structures in the cell. 



2. MATERIAL AND METHODS 



The material for the present study consists of a large series of 

 sea-urchin eggs, fixed before fertilization and at different stages 

 of their development after fertilization. The material has been 

 collected at the French biological station at Roscoff, whose kind 

 hospitality I highly appreciate. 



