SPH^ROPLEA. 



8l 



in the two varieties, as^will be shown, the cleavage is not the same. 

 In var. braunii the ring-like disposition of the protoplasm disappears, 

 while large vacuoles appear, transforming the entire cell-contents into 

 a foamy structure in which larger and smaller strands and masses 

 alternate (Fig. 27, B). In the dense portions of protoplasm nuclei, as 

 well as chromatophores and pyrenoids, are irregularly disposed. Now 

 a cleavage takes place by which the plasmic contents are segmented 

 into irregular protoplasts of varying sizes (Fig. 27, C). These proto- 

 plasts contract (the large vacuoles thereby gradually disappearing) and 



' V: <*'" 



FIG. 28. Parts of contents of young antheridia, showing 

 nuclear history preparatory to formation of sperma- 

 tozoids in S. braunii. (After Klebahn.) 



A, part of plasmic ring showing two nuclei in prophase of 



division. 



B, spindle stage of same mitosis. 



C, anaphase probably from second mitosis. 



D, Telophase of a later nuclear division. 



E, Condition of nuclei between successive mitoses, pyre- 



noids still present. 



F, nuclei shortly before formation of spermatozoids ; the 



pyrenoids have disappeared. 



round up to form the egg-cells, of which two to four are seen in a cross- 

 section of the cell. 



Neither shortly before nor during cleavage, according to Klebahn 

 ('99), is there to be observed a division or fusion of the nuclei, so that 

 (contrary to Rauwenhoff who claimed that during the formation of the 

 eggs the number of nuclei was diminished) each egg 1 may contain, in 

 addition to 2 or more pyrenoids, several nuclei, the number varying 

 from i to 5 (Fig. 29, A to E) . The number of nuclei falling to any 

 egg is largely a matter of chance, since the cleavage planes do not seem 

 to be determined in any way by the number or position of the nuclei 

 in the cytoplasm. 



1 The so-called " giant eggs " are exceptions. 



