290 Causes and Course of Organic Evolution 



s])ecial male characters that are hereditarily transmitted. 

 According to Baltzer the converse is true for the sea-urchin, 

 since it is the egg cell in it which forms the supplementary 

 sex chromosome. For recent synoptic literature on this, ref- 

 erence might be made to the papers of Morgan, published 

 during the past five years in "The American Naturalist" 

 and cognate journals; to his work on "Heredity and Sex" 

 (1918); and to Walters' "Genetics" of the same year. 



But in a minute critical study of plant and animal hybrids 

 as well as in the behavior of the male and female gametes 

 in process of fusion, also during subsequent divisions in for- 

 mation of the cell lineage, it becomes increasingly evident 

 that the two parental constituents evidently become physically 

 apposed m their colloid molecules, rather than chemically 

 blended, since varying degrees of separation, or of swaying 

 toward one or another parent, may occur in some one structure, 

 or in the organism as a whole. So the writer concluded, in 

 connection with the share that each sex-element might con- 

 tribute, that one of three conditions may exist in hybrids, 

 and present evidence generally indicates that the same is true 

 for individuals of a species: 



(1) Often "each sex element, after union with its comple- 

 mentary sex element, represents half its foimer individuality, 

 or retains half of its former hereditary properties." In this 

 case the resulting organism shows a minute blending of both 

 j)arental characters, but reduced by about half. 



(2) Where one or more physically or chemically diverse 

 substances, and therefore characters, are "found only in one 

 parent, and with no corresponding counterpart in the other," 

 these "are handed down though reduced by half." 



(3) Where one or more diverse physical or chemical char- 

 acters appear in each parent that "do not readily blend, each 

 may be reproduced by the hybrid but reduced by about half." 



Reviewing then the observed facts on which the above re- 

 suits were founded, the writer wrote: "Van Beneden (Rech. 

 siir la Maturation de I'oeuf. 1883) went further than most 

 of his zoological coworkers were prepared to go when he as- 



