ON THE ORIENTATION OF CENTRIOLES IN DIVIDING CELLS, AND ITS SIGNIFICANCE: A NEW CONTRIBUTION TO SPINDLE MECHANICS

¹ Department of Zoology, University of North Carolina, Chapel Hill, N. C., and the Marine Biological Laboratory, Woods Hole, Mass.

1. The centrioles of the egg of Polychoerus carmelensis, at first meiotic metaphase, second meiotic metaphase, and resting first cleavage metaphase, are slightly curved rods which are usually oriented at right angles to each other and to the main axis of the spindle.

2. Centriole orientation and behavior in the spermatocyte divisions of Gryllidae and Hemiptera, as described by Johnson (1931) and Payne (1927), in relation to the arrangements of daughter cells, are compared with centriole orientation and predicted behavior in the egg of Polychoerus.

3. These considerations (on centriole orientation and behavior) constitute the basis for a new hypothesis, as follows:

a. The orientation of the centrioles at any given division determines the position in which the daughter centrioles will separate from each other.

b. The path of separation of daughter centrioles determines the position of the main axis of the spindle for the next division.

c. The axis of the spindle determines the relative positions of the daughter cells with respect to each other.

d. This arrangement of the daughter cells is maintained, for a time at least, by the primary cell connective, of which the spindle remnant is the significant portion.

e. These relations obtain in the absence of secondary intervening factors.

4. The inherent right-angle orientation of the centrioles at the two poles of the first cleavage spindle of Polychoerus is thus interpreted in causal relation to the alternating dexiotropic and leiotropic divisions in spiral cleavage.