J. R. SHAVER 265 



1928; Agaiawal, 1949), but the distribution of various granular 

 constituents along axes, or into "organ-fonning" areas, of eggs is, 

 as has been pointed out on numerous occasions (Wilson, 1928; 

 Watterson, 1955), a result, rather than a cause, of the polarity of 

 the egg. Summarizing the earlier literature on the subject of 

 cytoplasmic inclusions of egg cells, Wilson (1928) states: "It is 

 important to bear in mind the rapid increase of chondriosomes 

 (and of Golgi bodies?) that takes place during the growth of the 

 egg. Only a part of them are used up in the production of other 

 formed elements. The greater number persist, possibly to play 

 some role in the fertilization of the egg, in any case to be handed 

 on to the embryonic cells by cleavage. Perhaps we catch here a 

 glimpse of a mechanism concerned not merely with yolk forma- 

 tion but with the general processes of determination, localization 

 and heredity." 



But it is precisely the significance for mechanisms of determi- 

 nation and localization of the cytoplasmic inclusions of egg cells 

 (not to mention the still problematical nature of inclusions trans- 

 ported into some egg cells by the sperm) that still eludes us. It 

 has been the universal result of centrifuging egg cells of both 

 mosaic and regulatory types, that the disarrangement of visible 

 cell inclusions, either slightly or quite drastically, does not appear 

 markedly to alter the development of the embryo. The extreme 

 case of this type of experiment is the well-known one of Harvey 

 (1946), whereby fragments of Arbacia eggs, presumably devoid 

 of any granular inclusions, developed into normal embryos after 

 fertilization. 



Two points may be mentioned in connection with this experi- 

 ment : 



1. Harvey states (1946) that mitochondria displaced from the 

 most centripetal egg fragment are replaced during development 

 by de novo formation of these particles, since the pluteus larva 

 developing from it can be seen to have mitochondria. Harvey, 

 however, described in the clear quarter-egg and the "white" 

 halves, a fine line of granules, which sometimes included small 

 fibers, which were thought to be microsomes (see Fig. 1). The 

 identification of mitochondria in the various fragments of centri- 



