88 CARNEGIE INSTITUTION OF WASHINGTON. 



it is clearly evident that contraction is not due in any way to the 

 myofibrils, as supposed by some, since no myofibrils are present in the 

 living cells ; nor can it be due to imbibition of water at the point of con- 

 traction, for in that case there would probably be no currents of proto- 

 plasm toward the point at which the changes take place. Moreover, 

 it is apparently not dependent upon the factors which are involved in 

 the formation of pseudopodia, since the latter were formed by the cell, 

 regardless of the fact that it was undergoing rhythmical contraction. 

 Mitosis was observed in contracting cells, and it is of interest to note 

 that during the division of the cell fibrils were not formed upon fixation. 



In the report of last year I referred to the investigations of Professor 

 W. H. Lewis, in which he showed that in the degeneration of fibro- 

 blasts in chick embryos granules and vacuoles are formed which, as 

 they increase in number, tend to accumulate about the centriole, 

 leaving a clear area, the centrosphere. This area may become as large 

 as the nucleus and is usually entirely free of the granules and vacuoles. 

 On continuing these studies Dr. Lewis finds that there are two types of 

 degeneration, both accompanied by enlargement of the centrosphere. 

 There is the vacuolar type, characterized by extensive vacuolization, 

 first about the centrosphere and finally throughout the entire cyto- 

 plasm. The centrosphere is enlarged, but usually without a sharp 

 border. The other type, the giant-centrosphere type, shows only a 

 slight or moderate vacuolization, and the enlarged centrosphere has a 

 sharp border and contains a single or double centriole surrounded by a 

 clear medullary and an outer cortical zone. The cortical zone may be 

 sharply limited or may continue out into the cytoplasmic framework 

 between the vacuoles. 



In studying the formation of the giant centrosphere it can be seen 

 that it develops gradually around the centriole. Preceding the appear- 

 ance of the centrosphere, the centriole is surrounded by degeneration 

 granules and vacuoles; as the centrosphere develops, these are forced 

 first to the periphery of the medullary zone and finally to the periphery 

 of the cortical zone. The mitochondria are oriented around the centro- 

 sphere, at first radially, later concentrically. These two forms of de- 

 generation are not sharply separated from one another and all grada- 

 tions between them are found in the mesenchyme cells. In cultures 

 from the same region sometimes one type and sometimes the other pre- 

 dominates. It is not yet clear whether the variations in appearance 

 are due to the cells themselves or to differences in the cultural environ- 

 ment. It seems probable that the centrosphere is semi-solid, as is also 

 the irregular cytoplasmic framework extending out from it to connect 

 with the semi-solid peripheral layer of the cell. The vacuoles and gran- 

 ules occupy the more fluid part of the cytoplasm, in which are pro- 

 duced currents that carry the passive granules back and forth. The 

 mitochondria lie in the cytoplasmic framework and hence their move- 



