ON THE DEVELOPMENT OF PARASITIC COPEPODS. 59 



The nuclear membrane of the protoplasmic cell dissolves in 

 the region of attachment of the mantle fibers, which then become 

 attached to the chromosomes. The remainder of the nuclear 

 wall, and the nucleolus dissolve and the chromosomes are ar- 

 ranged in the equatorial plate (Fig. 23), which is at first far 

 removed from the central spindle, but later the central spindle 

 assumes its normal position in the center of the peripheral spindle 

 (Fig. 24). The division divides the cell by a meridional (sagit- 

 tal) cleavage into equal daughter cells (a* and #*). 



In the yolk cell, as the attraction spheres separate they grow 

 in size (Figs. 21-24). The central spindle presses against the 

 nucleus, forming a groove (Fig. 22) which makes it appear as 

 though the nuclues was divided (maternal and paternal elements 

 distinct), but sections show that this division does not pass com- 

 pletely through the nuclues. The nucleus is drawn out to about 

 four times its original length (Fig. 23), one sphere moving faster 

 than the other and reaching the surface of the egg, on the right 

 side of the protoplasmic cell. 



This elongated nucleus is bent considerably and suggests that 

 it is being elongated by a force applied internally, and is bent by 

 external resistance, but I think the bending may be due to the 

 unequal pressure of the yolk, and the elongation of the nucleus 

 may be due wholly or in part, to the contraction and separation* 

 of the mantle fibers. The nuclear membrane dissolves, and 

 the equatorial plate is formed (Fig. 24). It is to be noted that 

 whereas the elongated nucleus is bent the fully formed spindle 

 is straight. In Fig. 23 it is seen that the end of the nucleus 

 attached to the peripheral sphere is enlarged and nearer to its 

 sphere than the other end is, probably due to increased tension 

 of the mantle fibers at this end, accompanied by pressure of the 

 yolk on the sides of the nucleus. 



On dissolution of the membrane all the nuclear sap goes into the 

 peripheral sphere. A yolk spherule is often caught between the 

 astral rays and the cell wall (Fig. 24, r 5 ). Protoplasm migrates 

 along the astral rays to the spheres. The division cuts off a small 

 protoplasmic cell from a large cell containing practically all the yolk 

 (d*). I have not worked out the cell lineage any further in this spe- 

 cies, though it appears to be essentially the same as the dichelestid. 



* By elongation of the central spindle? 



