Ill 



GERM-TRACK 



and gradually disappear, and a new set of granules makes its appearance 

 in the next prophase. As the granules of the preceding mitosis have not 

 quite disappeared by the time the new set develops, the cell is never 

 altogether without them, and this fact makes its continuous identification 

 possible. The new granules appearing at prophase are again concen- 



FIG. 39. 



Differentiation of the germ-track in Cyclops fuscus (A-H), and Diaptomus coeruleus (I). (After Amma, 

 /4.Z., 19".) A, prophase of first cleavage mitosis, granules congregated round one attraction sphere; B, 

 same mitosis, metaphase; C, 2 -cell stage, resting nuclei (note gonomery) ; D, prophase of second cleavage 

 division; E, i6-cell stage. All the nuclei have completed their division, and entered into the resting stage, 

 except that of the granule cell which is still in anaphase. F, division of the granule cell into the two 

 primitive germ-cells ; G, H, I, later stages. 



g, primitive germ-cells. 



trated round one attraction sphere only, and thus again pass into only 

 one of the daughter cells. A differential cell division of this sort takes 

 place four times, so that the cleaving egg up to the end of the i6-cell 

 stage contains one, and only one, cell with granules, or granule cell. The 

 nucleus of this cell does not as yet differ markedly from those of the other 

 cells, except that it constantly lags a little behind the others in mitosis. 



