384 



This is beautifully shown in the branching of the nuclei in certain 

 gland cells of insects to which Meckel, Zaddach, Carnoy, Korschelt 

 and others have called attention. This branching takes place during 

 phases of marked cytoplasmic activity and serves to increase the con- 

 tact surface of the nucleus thereby bringing the chromatin in the closest 

 possible relation to areas of cytoplasmic activity. 



In addition to the striking structural changes above mentioned 

 we should recall the noteworthy shifting in the position of the nuclei 

 during the phases of greatest cytoplasmic activity. At the time the 

 first fibrillae are formed, on the notochordal side of the muscle cell, 

 the nuclei are observed to occupy an axial position. As the differen- 

 tiation of the fibrillae continues from the inner toward the outer side 

 of the cell there is a corresponding movement of the nuclei toward 

 the outer side. Finally, when the cell is completely filled by the 

 newly formed fibrillae, we find the nuclei almost without exception on 

 the outer margin. 



In the adult we find no less changes remarkable in the posi- 

 tion of the nuclei since they not only lie at the periphery of the 

 cell but are likewise scattered throughout the cytoplasm, and show no 

 definite position either with reference to the planes of the animal or 

 to the axis or periphery of the cell itself. Why and how these nuclei 

 come to lie in the sarcoplasm is unknown. It is probable that with 

 the continued growth of the muscle cell the sphere of nuclear activity 

 becomes too far removed from that of cytoplasmic activity thereby 

 necessitating a redistribution of the nuclear material. 



It is possible, however, that the movement of the nucleus, from 

 the axis to the periphery of the cell is the result of mechanical 

 factors, in that the continued formation of fibrillae, from the inner to 

 the outer side of the cell, might cause an outward displacement of 

 the nuclei. To account for their later position among the fibrillae 

 through the influence of mechanical factors is exceedingly difficult. 



There are many observations which seem to conclusively show a 

 physiological correlation between nuclear movements and cytoplasmic 

 activities. The most familiar instances are found in the various gland 

 cells to which nearly all histologists have called attention. 



Here might also be cited the observations of Haberlandt who, 

 from an extended study of the relation of nucleus to cytoplasm in a 

 large number of plants, was led to the conclusion that the nucleus 

 moves to the area of greatest cytoplasmic activity, as in the thicke- 

 ning of the cell membrane, where it remains until the period of activity 

 ceases when it returns to its original position. 



