A THEORY OF HEREDITY 



UNDER the title " Perigenesis der Plastidule oder 

 die Wellenzeugung der Lebenstheilchen," Professor 

 Haeckel lias 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 Brticke, " 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 Mold's term, " protoplasma." Haeckel 

 proposes to distinguish the substance of the nucleus 



