PROTOPLASMIC MOVEMENT. 89 



of the pronuclei during maturation and fertilization. For 

 these active changes in the cytoplasm he proposed the name 

 cytokinesis. Morgan ('93) observed that the reddish pigment 

 granules found over the surface of the eggs of Arbacia move 

 entirely away from the micromere pole of the egg before the 

 micromeres are formed. In some eggs this movement begins 

 in the two-cell stage, and is carried on until the micromeres 

 are formed at the sixteen-cell stage. Nussbaum (^93) observed 

 in the division of entoderm and mesoderm cells of young em- 

 bryos of Rana temporaries that the brown-black pigment col- 

 lected in a ring around the equator of the dividing cell, and as 

 the division advanced the ring became narrower and deeper 

 until it formed a true cell plate between the daughter-cells. 

 Van Bambeke ('96) has observed a similar phenomenon in the 

 cleavage of the toad's egg. Gardiner ('95) observed in the eggs 

 of Polychoerus and Aphanostoma a reddish-yellow pigment 

 which, because of its form and peculiar movements, he sup- 

 posed might be some form of alga. After the egg is laid it 

 migrates from the centre toward the periphery, and forms a 

 girdle around the ovum in the plane of the first cleavage. A 

 similar line of pigment marks out the division plane of every 

 succeeding cleavage up to the ten-cell stage. He also observed 

 that these pigment granules migrated from one pole of the egg 

 to the other, though they never passed from one cell to the other. 

 These movements greatly impressed Gardiner with the won- 

 derfully active and powerful forces within the egg. When the 

 living egg is seen under an immersion lens he says "the sur- 

 face fairly scintillates with the movements of the protoplasm 

 and these pigment granules." 



About the same time Loeb ('95 1 ) suggested that a mechan- 

 ical explanation of the division of the egg or embryo was to be 

 found in diffusion and vortex movements of the protoplasm, 

 similar to those observed by Quincke in an emulsion of oil and 

 soda solution. "I conceive," says he, "that on the surface of 

 the egg, possibly in the meridian or circle whose plane sepa- 

 rates from one another the two radiating systems of the cen- 

 trosome, diffusion phenomena occur as soon as the nuclear 

 division has physically ended. These lead to the formation of 



