342 EDWIN G. CONKLIN 



protoplasmic cells at the vegetal pole, each of which is dividing 

 or has just divided, while the four macromeres are giving off a 

 second set of small protoplasmic cells at this pole. It is prob- 

 able that these small cells are micromeres (ectomeres) of the first 

 and second quartets. Figures 114, 116 to 122 were centrifuged 

 after the formation of the first quartet at the animal pole, which 

 is shown in faint or dotted outline in figures 114, 116, 118; in 

 figure 114 four protoplasmic cells, which probably represent the 

 second quartet, lie at the vegetal pole; in figure 116 the second 

 quartet cells are subdividing and a third quartet is being formed ; 

 in figure 117 are shown at the animal pole eight cells, four 'cen- 

 trals' and four 'turrets,' derived from the first quartet, while 

 twelve cells of the second and third quartets are shown in faint 

 outline at the vegetal pole; these twelve cells, which represent 

 eight cells of the second and four of the third quartet, are shown 

 in figure 118 as they are seen through the egg. 



If the small cells formed at the vegetal pole in the preceding 

 figures are really micromeres (ectomeres) it should be possible 

 to allow' the first quartet to form normally at the animal pole, 

 to then force the second quartet to form at the vegetal pole, 

 and finally to allow the third quartet to come back and form at 

 the animal pole. This is just what has happened in one or more 

 quadrants of the eggs shown in figures 119, 12l, 122; in these 

 three eggs the first quartet, which has now subdivided into four 

 'central' and four 'turret' cells, lies at the animal pole; the second 

 quartet, each cell of which has subdivided, lies in the furrows 

 between the macromeres on the vegetal side of the egg, while in 

 figures 121 and 122 the third quartet has formed outside the 

 first quartet on the animal side of the egg. There can be little 

 doubt, from the manner and time of division of the macro- 

 meres and micromeres in these eggs, that the micromeres on 

 the vegetal side of the egg are typical second quartet cells ex- 

 cept in respect to their position. On the other hand in figure 120 

 the first quartet was formed normally at the animal pole, 

 but centrifuging was not sufficiently strong to carry the nuclei or 

 mitotic figures for the fourth cleavage clear through the macro- 

 meres to the vegetal pole; as a result the fourth cleavage was a 



