GROWTH OF TISSUES OF THE CHICK EMBRYO 81 



Associated with this type of cellular growth is a constant thin- 

 ning and often a complete disappearance of the clot over the thicker 

 layer of the cells (fig. 3). Following this disappearance of the 

 fibrin a large drop of fluid collects on the lower surface of the drop. 

 This fluid is much in excess of the serum which could be squeezed 

 from a clot of plasma of the same size. Its formation is prob- 

 ably associated with the cellular growth. At these points where 

 fibrin has disappeared, the cells are most active, karyokinesis 

 being common (fig. 14). 



Actual division of the cells has never been completely followed 

 under the microscope. In the stained specimen, however, all 

 stages of mitotic division can be readily found in preparations 

 under six days old. The shape of the cell, as especially studied 

 in the spindle types, does not change during the prophase ; at the 

 period of metaphase, how^ever, it becomes round and remains in 

 this shape until the daughter cells are formed. Division of the 

 nucleus of a direct type has been seen only in giant cell formation, 

 which is common after the sixth day of growth. Active mitotic 

 division may continue for several days. I have seen manj- mitotic 

 figures in a few of the specimens fixed at the eighth day of culti- 

 vation. 



The study of the mesenchyme cells has demonstrated that the 

 plasmatic medium has power of preserving the life of the cell as 

 well as supplying sufficient nutriment for growth, as shown by 

 the active division of the cells. 



I wish to thank Prof. R. G. Harrison for the use of his labora- 

 tory and his many helpful suggestions throughout the course of 

 this work. I am also indebted to Dr. Alexis Carrel for many 

 valuable suggestions. 



The Jodrnal of Experimental Zoology, Vol. 10, No. 1 



