596 GRIFFIN. [Vol. XV. 



(PI. XXXI, Fig. 12) the outer aster is closely applied to the 

 inner wall of the membrane and often flattened against it. The 

 funnel-like depression of the egg surface next the outer centro- 

 sphere, not infrequently seen in other forms (notably Physa 

 and the mouse), is here quite noticeable. It is probably to be 

 referred to the influence of the aster, which causes the bound- 

 ing surface of the egg to conform to the radial arrangement. 



During the divergence of the daughter-chromosomes, the 

 respective halves are united by fibers considerably finer than 

 the traction-fibers, and which present a wavy and granular 

 appearance (PL XXXI, Fig. 15). These interzonal fibers (Ver- 

 bindungsfasern) are still present at telophase and can often be 

 traced from the chromosomes in the extruding polar body to 

 the corresponding ones within the egg. They soon disinte- 

 grate and break up into separate granules in the equatorial 

 region, though a cell-plate (zwischenkorper) is formed. 



b. The Second Polar Division. 



In mode of formation the second maturation amphiaster pre- 

 sents a marked contrast to the first. It arises shortly after the 

 chromosomes have reached the poles of the first polar spindle, 

 and apparently as a new formation between the already diverged 

 daughter-centrosomes in the previously clear and homogeneous 

 centrosphere {cf. Boveri, '90 ; Mead, '95 ; Korschelt, '95 ; Mac- 

 Farland, '97; and others). The chromosomes remain for some 

 time on the outer side of the spindle, stretching in a curved line 

 from pole to pole (PI. XXXI, Figs. 15-18). From now on, the 

 spindle steadily elongates until its definitive length {\ to l the 

 egg-diameter) is attained, and at no time shortens. A rotation 

 through 90 degrees of arc brings it radial with its outer aster 

 at the point on the egg surface at which the first polar body 

 was expelled. At division the extremely coarse, straight, and 

 homogeneous interzonal fibers are gathered together as the polar 

 body is constructed off, but the resulting cell plate disappears 

 shortly after separation of the body (PI. XXXII, Figs. 19-26). 



The inner centrosome has meanwhile divided exactly as 

 though preparing for a third mitosis (PI. XXXII, Figs. 19-26). 



