MORPHOCHORETIC PATTERN CLEAVAGE 



329 



Fig. 20. Distribution of mucopolysaccharides (MPS) as shown by metachromasia in vivo 

 and by other tests. The seriation and presentation of the stages is the same as in Fig. 17. 

 The specimens are shown as stained in vivo for 15 min. in a 2- 10"^ solution of toluidine blue, 

 at pH 7.5-8.0. The young oocyte (a) has only a few scattered granules. The fully grown 

 oocyte (b) has some discrete groups of MPS granules. The maturing unfertilized egg (c) 

 shows metachromasia in scattered granules and in large groups of reddish granules. 

 At the pronuclei stage (d) the reaction is especially intense in the vicinity of the pronuclei. 

 At the 2-cell stage, a large ball of positive granules accompanies each nucleus; MPS are 

 also present in the cortex and between the cells. At the 3-cell stage (fugace), the dividing 

 cell is distinctly less positive (f ) . At the 4-cell stage (g) more and larger MPS-loaded granules 

 are found, grouped together near the nuclei and at the surface of the blastomeres, especially 

 in the two larger ones. With the 8-cell stage (h) , the blastomeres are arranged in two distinct 

 groups, the 4 larger ones strongly metachromatic, containing columns of large positive 

 mitochondria. The symmetry becomes quite distinct. When these four large cells have 

 enveloped the smaller ones (i, j, k) the enveloping layer remains characterized by an intense 

 metachromasia. Nidation (1) does not noticeably change the picture. From Dalcq, 1955. 



first spindles (O. Hertwig rule). But this is only a partial view of the picture; 

 the true relations are more complex. 



Although these observations are only sporadic, they suggest that segmentation 

 is not independent of the morphochoretic pattern as is generally believed. In all 

 the cases so far mentioned, the two first furrows cut through the primary axis. 

 However, there is a remarkable exception to the rule in the case of the nematodes, 



Literature p. 483 



