PLATE 1 
EXPLANATION OF FIGURES 
1 Axial section of an unfertilized normal ovocyte of Nereis, fixed in Flem- 
ming’s fluid, weaker solution. In this fixing fluid the yolk granules swell and tend 
to run together. The oil drops are dissolved out in the preparation and are 
represented by empty spaces. v.m. vitelline membrane. c./. cortical layer, from 
which the jelly is formed. 
2 Section of an egg of Nereis, fixed in Meves’ fluid five minutes after insemina- 
tion. The cortical layer is already somewhat reduced in thickness. The yolk 
granules are not swollen. The oil drops are not dissolved out. The section is 
approximately horizontal. c.l., remains of cortical layer; v.m., vitelline membrane. 
3 Section of an egg of Nereis, fixed in Meves’ fluid fifteen minutes after insem- 
ination. The cortical layer has entirely disappeared, and the perivitelline space 
isformed. The germinal vesicle is breaking down and the first maturation spindle 
is forming. p.v. perivitelline space. v.m., vitelline membrane. 
4 Section of an egg of Nereis, fixed in Meves’ fluid fifty-seven minutes afeae 
insemination. Only one centrosome of the sperm amphiaster is shown. 
5 Section through the first cleavage-spindle of Nereis, normal, one hour and 
twenty-seven minutes after insemination. 
6 Tetrapolar second maturation spindle of Nereis. See text for description 
(p. 378). Three egg nuclei are formed in such a case. 
7 Egg nucleus of egg of Nereis in which the spermatozoon was removed by 
centrifuging. The chromosomes of the first cleavage are formed, but there are 
no asters. Cf. fig. 5 
All figures drawn with the camera lucida with Zeiss comp. oc. 6 and 2 mm. 
hom. oil im. obj. 
391 
