pitulation of phylogeny. This, says Haeckel, is what the 

 "fundamental Law of Biogenesis" teaches us. (The reader 

 of Haeckel and other Darwinians will frequently find laws 

 put forward to establish facts : whereas other men of 

 science prefer to have facts establish laws). When, there- 

 fore, as Quatrefages remarks, the transition between the 

 types which Haeckel has incorporated into his genealogical 

 tree, appears too abrupt, he often betakes himself to on- 

 togeny and describes the embryo in the corresponding in- 

 terval of development. This description he inserts in his 

 genealogical mosaic, by virtue of the "Law of Biogenesis." 

 Many theories have been constructed to explain the 

 phenomena of embryological development. Of these the 

 simplest and least mystical is that of His in the great 

 classic work on embryology, "Unsere Koerperform." His 

 tells us: "In the entire series of form.s which a developing 

 organism runs through, each form is the necessary antece- 

 dent step of the following. If the embryo is to reach the 

 complicated end-form, it must pass, step by step, through 

 the simpler ones. Each step of the series is the physiolog- 

 ical consequence of the preceding stage, and the necessary 

 condition for the following." But whatever theory be ac- 

 cepted by men of science, it is certainly not that proposed 

 by Haeckel. Carl Vogt after giving Haeckel's statement 

 of the "Law of Biogenesis" wrote : "This law which I long 

 held as well-founded, is absolutely and radically false." 

 Even Oskar Hertwig, perhaps the best knoAAoi of Haeckel's 

 former pupils, finds it necessary to change Haeckel's ex- 

 pression of the biogenetic law so that "a contradiction con- 



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