352 EDWIN G. CONKLIN 



evidence for or against these possibilities may be considered 

 briefly. 



1. Electric polarity: polarity of fused eggs. There is really 

 little or no evidence that cell polarity is of the nature of electric 

 polarity. Neither the entire egg nor any of its parts orients 

 with respect to a constant current passed through the water in 

 which eggs are placed, and none of the constituent parts of a 

 cell is moved or oriented by an electric current passed through 

 the cell itself unless that current is so strong that phenomena 

 of convection occur (see ConkUn, '12). 



A certain amount of light is thrown upon the nature of the 

 polarity of the egg by the effect on this polarity of the fusion 

 of two or more eggs. If this polarity were the result of electric 

 charges carried by colloidal particles or if it were due to differ- 

 ent properties of the cell membrane at the two poles, the polarity 

 of fused eggs should be the resultant of the polarities of its com- 

 ponents. On the other hand if the polarity is due to an internal 

 framework of protoplasm which is but slightly miscible with 

 other similar frameworks and which therefore preserves to a 

 great extent its identity, the original polarity of two or more 

 eggs would not be much changed by their fusion. The facts 

 show that the latter is the case. 



When eggs of Crepidula are strongly centrifuged they are 

 pressed closely together and frequently adhere to one another. 

 Very rarely they fuse together so that no boundaiy can be seen 

 between the two. Thus figure 106 represents two eggs which 

 fused together in the 4-cell stage along the plane indicated by 

 the dotted line. Each egg is now in the 8-cell stage and each 

 preserves its original polarity, as is shown by the polar bodies, 

 micromeres centrospheres and nuclei. Although each egg is in 

 the 8-cell stage, the fusion of three pairs of cells reduces the 

 total number of separate cell bodies to 6 macromeres and 7 

 micromeres. The nuclei and centrospheres of the fused cells are 

 quite distinct and even the cytoplasmic areas are partially 

 separated by a tongue of yolk. 



It rarely happens that eggs are fused together in experiments 

 with centrifugal force, and figure 106 represents one of these 



