No. 525] SEXUAL REPRODUCTION IN ALGJE 523 



side of nuclear membrane. Close to this point but out- 

 side of the nuclear membrane, there is developed an ac- 

 cumulation of kinoplasm from which is differentiated an 

 aster with a chromosome, so that the nucleus during 

 synapsis exhibits strongly marked polarity. 



The chromatic loops extend into the nuclear cavity and 

 sections show them to be thirty-two in number. After a 

 period of condensation each loop is transformed into a 

 pair of chromosomes by the separation of the arms at the 

 bend. The pairs of chromosomes then become scattered 

 through the nuclear cavity (diakinesis). The interpreta- 

 tion of this history is that the sixty-four somatic chromo- 

 somes of the Fucus plant are arranged end to end on the 

 spirem and become associated in thirty-two pairs through 

 the formation of the loops. Meanwhile a second aster 

 appears, apparently arising dc novo, generally at some 

 distance from the first, and the two asters establish the 

 poles of the first spindle. The thirty-two pairs of chro- 

 mosomes are gathered at the equatorial plate and the 

 members of the pairs distributed in two sets, thus affect- 

 ing a numerical reduction by one half of the sixty-four 

 somatic chromosomes. 



There is apparently no premature division of the chro- 

 mosomes in preparation for the succeeding division, as is 

 generally the case in the heterotypic mitosis. The sec- 

 ond and third divisions in the oogonium are similar in all 

 essentials to typical mitoses. They deal, of course, "with 

 thirty- two chromosomes, the haploid number, which 

 divide lengthwise during the metaphase of each mitosis. 

 There is a long period of rest following the second 

 mitosis. The first mitosis in the antheridium is likewise 

 a reduction division similar to that in the oogonium and 

 need not be described in this connection. 



The nucleus of the unfertilized egg exhibits no evi- 

 dence of polarity, but following the entrance of the sperm, 

 according to Vamanouchi, an aster with a centrosome 

 becomes at once evident. A second centrosome with 

 radiations appears later at the point where the sperm 



