KOFOID: DEVELOPMENT OF LIMAX. 57 
nomenclature of regarding the larger of two daughter cells as the mother, 
the smaller as the daughter. In reality both are daughter cells, and 
the mother cell has passed out of existence with their origin, a fact 
which a logical system of nomenclature of cell lineage must always 
recognize. 
SIXTH GENERATION, THIRTY-TWO CELLS. 
Following the formation of the sixteen cells of the previous generation 
there comes the usual rounded condition in which each blastomere asserts 
its individuality and diverges from its nearest of kin. This in turn is 
followed by the flattened condition, in which the spherical contour of 
the egg as à whole is restored. Itis during this period that the spindles 
which begin the formation of the sixth generation firsttappear. As in 
the previous generation there was a lack of synchronism in the cleavage 
of the two quartets 4.1 and 4.2, as shown in the nuclear conditions of 
Figures 20 and 21 (Plate III.), so here there is a similar separation 
of the divisions of this generation into two mitotic periods, the first 
appearing in the largest cells of the embryo, viz. the two quartets at 
the vegetative pole, aud resulting in the twenty-four-cell stage ; tho 
second involving the animal hemisphere, and resulting in the thirty-two- 
cell stage, thus realizing in this stage Warneck’s (50) conclusion that 
cleavage progresses according to the age of the cleavage spheres. The 
first phase is separated from the second by a period in which all the 
nuclei are in a resting condition. This period lasts some hours, and 
hence it is that cleavage stages killed at random contain a large pro- 
portion of eggs in the twenty-four-cell stage. 
Division of Quartet 5.1, forming 6.1 and 6.2. 
Plate III. Figs. 23-25; Plato IV. Figs, 27-32; Plate V. Figs. 33-36. 
Figure 23 (Plate TIL) shows a lateral view of an egg at tho completion 
of the first mitotic phase. The quartet 5.1 has divided, forming 6.1 and 
6.2. Applying the test asin previous generations, it is readily seen that 
this is a right spiral. The remnants of the nuclear spindle and the 
asters leave no question as to the relationship of the cells in this egg. 
The upper derivative lies to the right of the lower-one in every case. 
Reference to the quartets 6.1 and 6.2 in Figures 27-29, 31-34, 36, of 
four other eggs, shows the constancy of tho direction of this spiral. The 
division in this quartet is about equal, and is synchronous in tho four 
quadrants, 
