62 J. F. McCLENDON. 



Egg 



W< 



X 5 ' 2 



/a' 6 ' 2 (Primary germ cell). 



\/6-> (Entoblast). 

 TABLE OF CELL LINEAGE TO 32 CELL STAGE. 



II. ON THE NATURE OF THE CLEAVAGE PROCESS. 



Since Van Beneden in 1883 put forward the hypothesis that 

 separation of the chromosomes and division of the cell was 

 caused by contraction of the fibers of the karyokinetic figure, the 

 question of the mechanics of mitosis has aroused a great deal of 

 interest. The large size and peculiar form of the spindles in the 

 early cleavage of this egg, make them favorable objects for obser- 

 vations on this point. I have attempted to harmonize observa- 

 tions on the structure of coagulated colloids, and the modern 

 theory of the ultramicroscopic structure of colloids, with the 

 observations on artificially produced asters in colloids, and 

 asters and spindles appearing during mitosis in living cells. 

 A theory of Rhumbler and others as to the mechanics of the 

 formation of asters seems in general to be the only one applicable 

 to the observations I have made, yet I do not believe that this 

 theory is inseparable from the alveolar theory of the structure of 

 protoplasm. Asters can be produced in colloids which we have 

 no reason to believe have the alveolar structure in the strict sense. 

 According to Mann ('06), colloids consist of minute or ultrami- 

 croscopic particles suspended in a thin fluid. On congealing 

 (Hardy, Jour, of Physiol., V., 24), these particles by mutual at- 

 traction form rows which make up a meshwork (or interalveolar 

 structure ?) giving consistency to the mass. When colloids are 

 coagulated with substances (electrolytes) that act strongly and 

 quickly, the particles are large enough to be seen with the micro- 

 scope and are at first distributed homogeneously through the 

 fluid, but soon arrange themselves in rows which make up 

 a meshwork (" gerinnselbilder ' of Fischer). This passing of 

 a colloid from the "sol' to the "gel" or congealed state 

 may be hastened by addition of a fragment of coagulated colloid 

 to the former, in which case the rows of drops or particles 

 arrange themselves radially around the fragment, and an aster is 



