8o 



FECUNDATION ; HETEROGAMETES. 



former. These plasmic rings or diaphragms communicate with each 

 other by plasmic strands or bridges. In the plasmic rings are located 

 the rounded chloroplasts, pyrenoids and the nuclei. Of the latter the 

 number in each ring varies from 3 to 20 in var. braunii and from i to 4 

 in var. crassisepta (Fig. 27, A). 



In those cells in which spermatozoids are developed the nuclei 

 undergo four or five karyokinetic divisions, 1 so that ultimately about 

 300 small nuclei are present in each band (Fig. 28, A to F). During 

 these divisions the pyrenoids disappear, and the chromatophores 

 undergo several divisions and assume a pale, yellowish-brown color. 



FIG. 27. Cell-cleavage leading to formation of egg-cells in Spheeroplea braunii. ( After Klebahn.) 



A, outer view of a protoplasmic ring of a vegetative cell, showing chromatophores, pyrenoids and nuclei. 



B, portion of an oSgonium showing frothy nature of protoplasm and early stages of cleavage. 



C, small portion of oogonium, showing irregular protoplasts resulting from cleavage, which contain 



several nuclei and pyrenoids. 



The plasmic rings up to this time retain their original form. Now 

 the cytoplasm segments into numerous protoplasts, the spermatozoids, 

 in such a manner that each spermatozoid receives only one nucleus 

 (Fig. 29, I, J, K, L). The mature spermatozoids (var. crassisepta) 

 are as a rule spindle-shaped, being smaller at the anterior end, which 

 bears the two cilia. Near the middle lies the very small and densely 

 staining nucleus (Fig. 29, L). Kny in his Wandtafel, LXIII, figures 

 four or five yellowish chromatophores in each spermatozoid. 



The processes leading to the formation of the egg-cells show a 

 marked difference from those taking place in the antheridium. Even 



1 For details of karyokinesis tee Klebahn, '99. 



