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groups through geologic time, although I have tried to analyze the 

 behavior of all kinds of characteristics, I have failed to find any 

 such distinctions. If Weismann's theory is true, it ought to be 

 practicable to isolate in each type some class or classes of modifica- 

 tions that would be distinguished by the fact that they were not 

 inherited. 



It is practicable to isolate inherited characters from new variations 

 , which have not become fixed in any phylum. It is also practicable 

 to point out characters which are transient in various ways appear- 

 ing in individuals but not in varieties, in species but not in genera, 

 and so on. When one has by this system of exclusion arrived at 

 the end of the list, he finds that there is no class of characteristics 

 which may be described as non-inheritable. The new variations of 

 any one horizon which can be isolated from inherited ones are not 

 distinguishable in any way from others which occurred previously. 

 Later in time these new variations in their turn become incorporated 

 with the younger stages of descendants. The transient characters 

 of the zoon also do not differ in any way from others that are 

 inherited in allied species, genera, etc. For example, the position 

 of the siphuncle is very variable in some species of Nautiloidea, in 

 others of the same order it is invariable within a certain range, and 

 finally, in other species and genera it is invariable. In the Ammon- 

 oidea, derived from the same common stock as the Nautiloidea, this 

 organ attains a fixed structure and is invariably ventral from the 

 Devonian to the end of the Cretaceous, although in number of 

 forms and genera the ammonoids far exceed the nautiloids. All 

 characteristics, even those observable in some groups only in old 

 age, are found in the adults of other groups, and finally in the 

 young of the descendants of these, according to the law of tachy- 

 genesis. Everything is inherited or is inheritable, so far as can be 

 judged by the behavior of characteristics. Cope has ably sustained 

 this opinion in all his writings and has called it the theory of 

 " diplogenesis " in allusion to the essentially double nature of the 

 characteristics first ctetic and then genie. 



It is probable that what has been called effort is the principal 

 internal agent of organic changes as first stated by Lamarck, and 

 subsequently rediscovered and first maintained by Cope and subse- 

 quently by others in this country. The modern school of dynam- 

 ical evolution, or the Neolamarckian school, which has adopted this 



