CYTOPLASMIC INHERITANCE 225 



cleavage, and the pattern, or relative positions and pro- 

 portions of future organs, being foreshadowed in the cyto- 

 plasm of the egg-cell, while only the differentiations of 

 later development are influenced by the sperm. In short, 

 the egg cytoplasm fixes the general type of development, 

 and the sperm and egg nuclei supply only the details.'^ 

 If, as implied, the egg nucleus at first has already pro- 

 duced its effect on the cytoplasm, it has done something 

 more than supply the details ; and as to the sperm nucleus 

 I should substitute nearly all the stages of development 

 later than the gastrula. Moreover, sex is certainly one 

 of the fundamental characters of the organism, yet it 

 appearsi to be determined at fertilization by the chromo- 

 somal combination formed at that time. Conklin later 

 abandoned his earlier interpretation. 



Quite recently, in his book on ''The Organism as a 

 Whole,'' Loeb has discussed the question as to whether 

 the protoplasm of the egg is ''the future embryo in the 

 rough, ' ' the sperm furnishing only the ' ' individual charac- 

 ters. ' ' Loeb suggests that the ' ' specificity of the species ' ' 

 must be due to their proteins, and that the "heredity of the 

 genus is determined by proteins of a definite constitution 

 differing from the proteins of other genera. This consti- 

 tution of the proteins would therefore be responsible for 

 the genus heredity. The different species of a genus have 

 all the same genus proteins, but the proteins of the species 

 of the same genus are apparently different again in chemi- 

 cal constitution and hence may give rise to the specific bio- 

 logical or immunity reactions. ' ' The possible relations of 

 these considerations to heredity are summed up in the 

 following paragraph : 



It is thus doubtful whether or not any of the constituents of the 

 nucleus contribute to the determination of the species. This in its 

 ultimate consequences might lead to the idea that the Mendelian charaxi- 

 ters which are equally transmitted by egg and spermatozoon determine 

 the individual or variety heredity, but not the genus or species heredity. 

 It is, in our present state of knowledge, impossible to cause a spermato- 

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