OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 553 



like its mate, the division is not a reductional one in the Weis- 

 mannian sense, but must be equational. Owing to the pseudo- 

 reduction by conjugation in the prophase, the longitudinal 

 division along a plane which does not separate the conjugated 

 halves — and such is the case in A, canis — can only cause a reduc- 

 tion in the mass, not in the qualities of the chromosomes. 



d. Telophase. As the chromosomes come near the poles of 

 the spindle (fig. 42), the outer end of the latter, lying in contact 

 with the fertilization membrane, is cut off, partly by constriction 

 and partly by the formation of a dividing membrane (figs. 43 

 and 44). The chromosomes remaining within the egg substance 

 do riot ordinarily clump together and lose their individuality, 

 as do those which enter the polar cell (fig. 44). The group of 

 eighteen daughter tetrads in the egg organizes a new nucleus 

 with only a very transient nuclear membrane. Rarely the rem- 

 nants of the old interzonal fibers can be seen (fig. 44) . The cen- 

 trosome divides, its halves move apart, and, as the nuclear mem- 

 brane fades away, take up their position at the poles of the new 

 spindle (figs. 45 and46), which at first lies with its long axis parallel 

 to a tangent to the surface of the egg at that point. This proce- 

 dure differs from that followed in the spermatocytes of this 

 species, and usually also in both types of A. megalocephala, in 

 that the intermediate stage here possesses a nuclear membrane. 

 This newly formed spindle rotates through an angle of ninety 

 degrees and assumes a position perpendicular to the tangent to 

 the surface of the egg at that point (fig. 47) and is ready for the 

 second maturation division. 



During the formation of the first polar cell, the numerous 

 large, peripheral vacuoles in the cytoplasm fuse and cause it to 

 shrink away from the fertilization membrane. When this 

 shrinkage occurs, the first polar cell is left attached to the inner 

 surface of the fertilization membrane. This shrinkage also may 

 allow a slight rotation of the cytoplasm within the membrane, 

 so that the second polar cell may be given off apparently at 

 another position on the surface of the egg. This rotation may 

 reach a magnitude of twenty or more degrees (figs. 47 and 48), 

 and rarely the second polar cell seems to lie at the pole of the 

 egg opposite that at which the first was formed. 



