ON THE DEVELOPMENT OF PARASITIC COPEPODS. 6 1 



sion of the yolk cell (c/ u ) cuts off a protoplasmic cell d 5 - 2 (Fig. 

 31) to the right of the cap of protoplasmic cells; d 4 - 2 divides 

 equatorially, C 4 and ^ 4>1 transverselsy ; a 4A divides obliquely 

 but the daughter cells (a r>A and <? 5 - 2 , Fig. 31) come to lie one 

 behind the other. 



On the dorsal side <?'- 2 , < 4 - 2 , and O " divide transversely. 



Fig. 30 is an enlarged view of the spindle in the yolk cell, con- 

 structed from the two consecutive sections. The astral rays are 

 only partially shown, and, connecting them, the alveolar (or 

 reticular ?) hyaloplasm between the yolk spheres is represented 

 by dotted lines. This is a little later stage than Fig. 29 and the 

 spindle has shortened more. The distinctness of the centro- 

 somes is exaggerated in the figure, in fact it is doubtful whether 

 we deal here with centrosomes, but that the sphere is denser in 

 the center can be shown in some cases with Hermann's safranin- 

 gentian violet stain. 



E. FiftJi Cleavage (Figs. 3 1-35). --Of this cleavage I have 

 not enough stages to be sure of the lineage of every cell. There 

 are many disarrangements due to the cells extending over the 

 yolk and slipping on one another, which makes their lineage ex- 

 tremely difficult to follow. In the figures I have divided the 

 derivatives of a, b, c and d by heavy lines, and by comparing 

 Figs. 31 and 32, one can see the great change that has come 

 about. 



In this cleavage the yolk cell divides, giving off (near the 

 center of the ventral side) the last protoplasmic cell d 6 - 2 (Fig. 32), 

 which is the primary germ cell. 



F. Sixth Cleavage. In the fifth cleavage the divisions were 

 not synchronous, in the sixth cleavage the division of two cells, 

 d^ (the primary germ cell) and d 6 - 1 (the primary entoderm cell) 

 is delayed until some of the other cells are dividing for the 

 eighth time. After cleavage of the majority of the cells (Fig. 

 33) the blastoderm stretches over the yolk until it has half cov- 

 ered the latter (Fig. 34). During this process some derivatives 

 of d at each side of the egg and at the end of the blastoderm, 

 come to lie under the others and give rise to mesoderm. The 

 yolk cell (entoderm) divides totally by a sagittal furrow (Figs. 

 34, 35) and the primary germ cell sinks beneath the blastoderm 

 and divides by a sagittal furrow into two cells of unequal size. 



