GROWTH OF TISSUES OF THE CHICK EMBRYO 77 



plasma. In the latter they appear as continuous layers, as long 

 chains of cells, or as isolated single cells. The outhne of the cell 

 is indefinite during the early periods of active growth, especially 

 in the layers of cells where active division is taking place. They 

 have a pale homogeneous protoplasm filled in part by a single 

 horizontal layer of small, uniform and highly refractile granules. 

 These granules are scattered iriegularly throughout the cell in 

 small masses or long rows. The nucleus is well defined from the 

 remaining part of the cell by its great transparency, its freedom 

 from granules and its one or more round or dumb-bell shaped 

 nucleoli, which present a slightly opaque translucence. 



The growth of these cells in the plasma consists in a wandering 

 out of cells singly or in small masses from the tissues associated 

 with active division and multiplication. The movement of the 

 cells is very slow. Changes in shape, position and arrangement 

 of granules are only noted by the comparison of repeated obser- 

 vations. The tension of the cell throughout this movement is 

 noticeably undisturbed. The existence of a cellular tension is 

 shown by a constant maintainance of the sharp pointed process, 

 the flat contour and the scattered arrangement of its granules. 

 The association of this tension with the surrounding firm medium 

 becomes evident by suddenly jarring the cell and breaking it fiee 

 from its fibrin attachments. Such cells immediately assume a 

 spherical form. The granules appear at many levels and com- 

 pletely fill the cell, obscuring the nucleus. The activity, however, is 

 not always lost in these cells. Very quickly, amoeboid movements 

 similar to those seen in leucocytes, are obseived. New attach- 

 ments to the fibrin are made and the broad tense contour is re- 

 established. The movements of the cells in this condition of firm 

 attachment to the fibrin of the culture, as seen above, are dis- 

 tinctly different from those seen in leucocytes. A large number of 

 these cells never regained their form but remained inactive, soon 

 showing signs of degeneration. The cells which regained their 

 form were always in contact with the fibrin at some part of their 

 periphery. The importance of this fibrin supporting network 

 is without question from this observation as well as from obser- 

 vations on tissues planted in serum or very fluid clots. These 



