1897] FUNDAMENTAL PRINCIPLES OF HEREDITY 315 



come within the purview of the present article. As it is, the 

 theory falls under the ever-trenchant blade of Occam's razor, 

 " Entia non sunt multiplicanda praeter necessitatem." 



The antagonistic school, of Herbert Spencer, regard Living Beings 

 as characterised by their continuous adjustment of internal relations 

 to external conditions, and cannot see a priori grounds for regarding 

 the reproductive cells as especially lacking in this power of 

 adaptation. They regard instinct as only explicable as habit 

 transmitted and relatively fixed by constant transmission from one 

 generation to the next, and are disinclined to admit (even as a formal 

 hypothesis) any scheme that leaves all such considerations on one 

 side. They therefore are compelled to refer variations in the offspring 

 to the adaptive reaction of the parent to the environment, and hold 

 that there must be some mechanism of transmission other than 

 that of direct cellular inheritance, by which the reproductive 

 cells hand clown to their differentiated cell-offspring the characters 

 of the corresponding cells in the parent organism as a whole. 



Charles Darwin felt this need so keenly (in a way largely ignored 

 by those who style themselves his only true disciples) that he for- 

 mulated his elaborate provisional hypothesis of Pangenesis to supply 

 the mechanism that he postulated. He supposed that every cell in 

 the body gave forth minute buds or ' gemmules ' which circulated in 

 the blood, and were carried by its current to the reproductive cells 

 where they were stored up, and that in the development of the embryo 

 they induced the formation of cells like those from which they were 

 given off. Galton tried the crucial experiment of transfusing blood 

 from one breed of rabbits to another, and found that this had no 

 effect on the purity of the offspring. This not only shattered the 

 theory of Pangenesis, but settled in the negative every conceivable 

 theory of hereditary transmission based on the conveyance of formed 

 material particles or of chemical substances from the other parts 

 of the colonial organism to the reproductive cells. 1 



The second theory is that of Herbert Spencer, of 'biological units,' 

 of definite form and relation, which by their polarity tend to complete 

 the organism. I shall describe that development of it recently put 

 forward with great skill and ingenuity by Wilhelm Haacke under 

 the title of the " Gemmaria theory." 2 He holds that all living 

 plasma is composed of minute units, the ' gemmae,' grouped 

 together in aggregates, the ' gemmaria,' both being of definite form 

 and size, in virtue of which they tend to assume certain relations of 



^'Life and Habit," Loud. 1878; and "Unconscious Memory" (Lond., 1890). 

 The latter work contains a translation of Hering's paper. " A Theory of Development 

 and Heredity," by Henry B. Orr (London and New York, 1893), is written essentially 

 from this point of view. 



2 See "Gestaltung und Vererbung," Leipzig, 1893, and "Schopfung der Tierwelt." 

 Both these works arc written in a German style of exceptional charm, ease, and 

 vivacity. 



