1896.] ^^ [Conklin. 



the phylogenetic alterations of an animal form the end stages are not 

 alone altered, but the entire series from the egg cell to the end stage. 

 Every alteration of an end stage or addition of a new one must he 

 caused by an alteration of the egg cell itself." Nageli* has expressed 

 a similar view in the following famous sentence : "Egg cells must con- 

 tain all the essential characteristics of the species as perfectly as do 

 adult organisms, and hence they must difter from one another, no less 

 as egg cells than in the fully developed state. The species is con- 

 tained in the egg of the hen as completely as in the hen, and the hen's 

 egg difl'ers as much from the frog's egg as the hen from the frog." 



4. The remarkable tenacity of inheritance, as shown especially in 

 reversions and the preservation of useless and embryonic characters 

 through many hundreds or thousands of generations, and amid the 

 most diverse circumstances, bears strong testimony to the great stability 

 of that living structure which is the basis of inheritance. On the other 

 hand, all experience goes to prove that the living substance of the body 

 cells in general is readily modified, and that in a surprisingly short 

 time. The fact of this great difference cannot fail to be recognized ; its 

 cause is at present merely a matter of conjecture. 



Weismann at one time supposed the cause of this to be an absolutely 

 stable, absolutely separate, and perpetually continuous germ plasm. 

 However, there is the most convincing and abundant evidence that 

 although the germ plasm is relatively very stable and continuous, it 

 does not possess those divinely perfect characters ascribed to it. More 

 recently Weismann has expressly abandoned each and all of these 

 characters,! and now, like a good Lamarckian, finds "the cause of 

 hereditary variation in the direct eflects of external influences on the 

 biophores and determinants." 



The outcome of the whole matter, then, is that we find ourselves 

 much in U^e same position as we were before Weismann denied the 

 possibility of the inheritance of acquired characters. All hereditary va- 

 riations are caused by the action of extrinsic forces on the germinal proto- 

 plasm, producing changes in its structure. Strangelj^ enough, this propo- 

 sition was admitted as a logical necessity by one who undertook by 

 rigorous logic to prove the reverse. Since almost the only objection to 

 this position was the one raised by Weismann, it may now be considered 

 as definitely settled,- and the only question before us, then, is : How can 

 extrinsic causes modify the structure of the germinal protoplasm? 



Since by his own admissions, as Romanes has shown, the most char- 

 acteristic features of Weismann 's system, both as to inheritance and 

 evolution, have been virtually abandoned, it seems to some that his 

 theories have been of no real value, and that, like an ignis fatuus, they 

 have only served to lead biologists astray far from the path of science 

 into the dangerous quagmires of speculation. I do not share any such 



* Nageli, Mechanisch-physiologwche Theorie der Abstanunungslehre, 1884. 

 t See Romanes' Examination of Wcismannism, 18t)3. 



