connection (Figure 36, e and g) . The formation of micromeres, 

 according to Grube's description, is accompanied by the 

 replacement of substances inside the ovum segments; he 

 described these replacements in detail, alternating the 

 statement of facts about his observations with theoretical 

 conjecture about the forces of attraction, points of their 

 application, and so on. 



The micromeres, accumulated on the active pole, do not 

 exhibit equal size; the smaller they are, there are relatively 

 larger molecular substances (protoplasm) anc i smaller fatty 

 globules (yolk) in them. The smallest consist only of proto- 

 plasm and a round transparent nuclear body. These micromeres, 

 according to Grube, never arise from macromeres; therefore, 

 he wrote, "I must conclude that the small globules originate 

 from those large globules already present on the pole which 

 earlier separated from segments of yolk" (p. 22). The 

 accumulation of micromeres forms a plate in the form of an 

 isosceles triangle, without sharp limits passing into the 

 other surface of the ovum. This plate, which Grube called 

 the embryonic field, is so situated that the summit of the 

 triangle is turned toward the active pole and corresponds 

 to the cephalic part of the future embryo. 



It consists of "mosaic pieces" which arise as a result 

 of the multiplication of micromeres; in addition, these 

 pieces are smallest when they are nearest to the cephalic 

 end. In the stage described, not only the anterior and 

 posterior ends of the embryo, but also its upper and lower 

 sides, as the surface of the embryo, on which the embryonic 

 fluid is situated, correspond to its abdominal side. Using 

 the descriptive phrase "mosaic pieces", Grube resolved 

 consciously to avoid using the term cell, not being sure 

 that it inherits its own features, which are characteristic 

 of typical, in particular plant, cells. 



The anterior end of the embryonic field quickly expands 

 (Figure 36, c) , and by forming two summits it produces S-shaped 

 curved shafts (Figure 36, j), which Grube called the abdominal 

 shafts. This name is well-founded, because these shafts, 

 appearing in the field of the active hemisphere of the ovum, 

 i.e. the future dorsal side of the embryo, are displaced 

 towards its ventral side, where they later accrete into a 



523 



