44 J- F - McCLENDOX. 



C. Pandarns sinuatits. - - The oocyte of Pandarus si mi at us 

 differs from that of the dichelestid in that a single nucleolus is 

 formed, about equal in bulk to that of the several nucleoli of the 

 latter species together. The oocyte of the former is much more 

 compressed (thinner) than that of the latter. 



2. Maturation. 



A. Pandarus sinuatits. - - At the end of the growth period 

 the nucleus becomes irregular in outline which gives it a shrunken 

 appearance. The nucleolus becomes vacuolated and the nuclear 

 sap intensely staining. The location of chromatin cannot be 

 made out very well, but in thin sections chromatic threads can 

 be seen radiating from the nucleolus. Soon the nuclear sap 

 fades enough to show that the chromatic threads have split 

 (Fig. 6). The nuclear wall is dissolved. Sometimes the vacuoles 

 in the nucleolus increase very much in size and fuse into one. 

 In preparations of the entire oocyte the chromatic thread can be 

 seen to be divided into eight double chromosomes (Fig. 5). By 

 shortening of these double-rod-shaped chromosomes, ring-shaped 

 chromosomes are formed (Fig. 7). A transverse constriction 

 transforms the diad into a tetrad, that is a ring constricted at 

 four equidistant points, the two opposite constrictions, represent- 

 ing the divisions between the original rods, being deeper than 

 the other two. The spindle when first formed is longer than the 

 shortest diameter of the egg. It is similar to that found in free 

 living copepods, having no polar rays. The dense protoplasm 

 at each end of the spindle (Figs. 7 and 9) may possibly be de- 

 rived from archoplasm of preceding divisions, and it shows a 

 striking resemblance to the pole plates of the dividing nucleus in 

 Protozoa. The spindle is at first parallel to the flat surfaces of 

 the egg and rotates to an almost vertical position (Fig. 8). The 

 first polar body is very small and is extruded between the egg 

 and its neighbor at about the center of the flat surface that is 

 posterior (in relation to the mother) (Figs. 9 and 10). The 

 second polar spindle is smaller than the first. It is at first 

 parallel to the flat surfaces of the egg and rotates nearly to a 

 perpendicular position under the first polar body (Figs. 9 and 

 10). I have not seen the second polar body being cut off and 



