DIFFERENTIATION, HEREDITY, SEX 275 



been occurring normally, although ultimately a normal larva 

 may be formed (Fig. 127). 



The idea that these differentiated materials of the cytoplasm 

 really play the role of organ-forming substances in develop- 

 ment, is opposed by some (Lillie, Morgan, and others). The 

 opposed idea rests upon the experimental evidence that, 

 briefly stated, the really primary and fundamental organization 

 of the egg cytoplasm concerns the ground substance of the 

 protoplasm; the arrangement of the various formed stuffs 

 coincides with a similar and primary polarity and organization 

 of this fundamental protoplasmic matrix. This structure is 

 less manifest, but is really the factor which determines the 

 arrangement of the suspended cytoplasmic and deutoplasmic 

 granules and vacuoles. The correspondence between the 

 arrangement of these stuffs and the organ-forming substances 

 proper, is thus unessential, for the localization of the germ is 

 primarily a localization of the ground substance. In other 

 words, the varieties of material described by Conklin in Cynthia, 

 for example, are only secondarily related to the later differen- 

 tiation of particular organs or tissues, and their arrangement 

 is dependent upon the same primary factor that determines the 

 arrangement of the organs and tissues. 



The evidence for this view is found chiefly in the results of 

 certain experiments upon the eggs of Choetopterus (Lillie) and 

 Arbacia (Morgan and Spooner). The granules which give 

 character to the various regions of the cytoplasm differ in 

 specific density, and consequently can be thrown, by centrifu- 

 gal force, into abnormal regions of the ovum. When this 

 is done normal cleavage and development may proceed, normal 

 with respect to the original polarity of the ovum and not with 

 respect to the new polarity as indicated by the altered arrange- 

 ment of the plasmas. 



To illustrate, the egg of the sea-urchin Arbacia, contains four 

 different kinds of substance; one of these is distinguished by 

 the presence of bright orange or reddish pigment. In normal 

 development this substance lies toward the lower pole and 

 becomes localized in the lower quartet, so that when the micro- 



