A THEORY OF HEREDITY 



Under the title '' Perio^enesis der Plastidule oder 

 die Wellenzeugung der Lebenstheilchen," Professor 

 Haeckel has published quite recently a pamphlet con- 

 taining an attempt to furnish a mechanical explanation 

 of the elementary phenomena of reproduction which 

 shall be more satisfactory than Mr. Darwin's ingenious 

 and well-known theory of Pangenesis. I shall en- 

 deavour to show that Professor Haeckel's theory is 

 essentially that with which both English and German 

 students of Mr. Herbert Spencer's works have long been 

 familiar ; and that it does not furnish a clearer explana- 

 tion than does Mr. Darwin's Pangenesis, of the special 

 facts of heredity which Mr. Darwin had in view. 



Haeckel commences with a very concise statement 

 of what is at present known as to the visible compo- 

 sition of " plastids," those corpuscles of life- stuff called 

 "cells" by Schleiden and Schwann, "elementary 

 organisms " by Briicke, " life-units " by Darwin. Most 

 plastids possess a differentiated central kernel or 

 nucleus, which again possesses one or more nucleoli. 

 The substance of which the body of such a nucleated 

 plastid or true cell is mainly composed is generally 

 known by von Mohl's term, " protoplasma. " Haeckel 

 proposes to distinguish the substance of the nucleus 



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