385 
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 soon. 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 zodn 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 genic. 
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 
PROC. AMER. PHILOS. SOC. XXxII. 142. 2 W. PRINTED JUNE 5, 1894. 
