The Cytoplasm as Specific Substrate 199 



what I meant by calling these, in a sense, models of cytoplasmic 

 heredity: it might be supposed that in other cases counterclockwise 

 cytoplasmic orientation was a hereditary cytoplasmic property inde- 

 pendent of nuclear control. (Actually no such case is known.) 



It is rather probable, but not proved, that the determination of 

 the germ track in animals belongs to this group, but the facts are not 

 accessible to genetic experimentation. In a number of animals 

 (Diptera, Copepoda, Sagitta, Ascaris) the part of the egg cytoplasm 

 which will later supply the cytoplasm of the germ-track cells is already 

 visibly different in the unfertilized egg (predetermined). It may be 

 safely assumed, though it cannot be proved, that this differentiation, 

 which takes place during oogenesis, and all other predeterminations 

 found by experimental embryology are under genie control, just as in 

 maternal inheritance. Actually, here the cytoplasmic conditioning be- 

 comes visible in the production of stainable substances, the "germ- 

 track determiners" which stay strictly within the future germ-track 

 cells in subsequent development. From Boveri's classic work on 

 chromatin diminution in Ascaris we know that the conditioned cyto- 

 plasm in this organism even affects the behavior of the chromosomes 

 (controls the occurrence or absence of chromatin diminution; see 

 I 2 C fo). Thus we have a lasting cytoplasmic function of a deter- 

 minative nature, once the cytoplasmic difference is established. Again 

 we see why we may consider this a model of real cytoplasmic in- 

 heritance of the plasmon type. 



The most extreme cases of conditioning of the cytoplasm of the 

 egg prior to fertilization by genie (nuclear) action are found in the 

 realm of sex determination. We call these the most extreme cases, 

 because here the conditioned cytoplasm is important for sex deter- 

 mination; an all-pervading feature of the organism, it affects prac- 

 tically all development and every single cell. A typical case is that of 

 Lymantria dispar, the gypsy moth. The female determiners are located 

 in the Y-chromosome and, since the female is heterogametic, all eggs 

 contain a Y-chromosome up to meiosis. The male thus has no 

 Y-chromosome and no female determiners after fertilization of the egg 

 from which it develops. Males, however, may become intersexual (in- 

 cluding complete sex reversal), and it can be shown that the too 

 strong female determiners responsible are located in the Y-chromo- 

 some ( Goldschmidt, 1920c ff.; last discussion, 1953fl). In the silkworm 

 the female determiners in the Y are so strong that the presence of a 

 Y-chromosome produces a female* even when many male determiners 

 ( X-chromosomes ) are present (Tazima, 1943, 1944). Therefore, the 



