589 
hold in abeyance the inherent tendency to become coiled in the 
genus Orthoceras. This is more obvious when one considers that 
this trunk form is perpetually giving rise to branches that show the 
tendency to coil up. In assuming that habit is the cause as deter- 
mined by the law explained in the Introduction, p. 367, the greatest 
difficulty seems to disappear. As long as the shells could maintain 
themselves in the station they have been forced into, or had chosen, 
just so long would they maintain the form suitable for their habits 
or surroundings and they would change only in proportion as they 
changed their stations. Thus the main line might continue as long 
as it existed to hold the same form while its branches seeking new 
habitats and novel modes of life would change in directions deter- 
mined by those. Whatever the causes may be, the fact is obvious, 
that the tendency towards becoming arcuate and coiled is general 
in the descendants of straight shells and not confined to any special 
series or time. 
That it is an acquired character seems also to be a reasonable 
conclusion, An acquired character is one that is introduced into 
the life of the individual and is not present in the embryo before 
the tissues become differentiated into germ plasm and somato 
plasm. It is impossible to disprove or prove that a characteristic 
is acquired or genetic unless it can be followed back to its origin. 
Until this is done one cannot assert positively that it was not 
potentially existent in the embryo and became apparent at the 
proper time in the ontogeny in accordance with genetic law. 
The law of acceleration can be true only upon condition that 
there are such things as acquired characteristics introduced in 
epembryonic stages. ‘The examples given above in support of this 
law are all instances of acquired characters introduced late in the 
ontogeny and gradually forced back to younger and younger stages 
in successive generations, or species, or genera. ‘This law is based 
upon the assumption that such characteristics exist and it is also 
supposed to show the mode in which they are inherited. 
It is not necessary for me here to deal with any of these facts, 
except the tendency towards coiling among shell-covered Cephalo- 
pods. ‘This tendency is manifested in the conch alone of the Nau- 
tiloidea, that is, in the epembryonic stages, and we can follow it as 
described above, both in the phylogeny and ontogeny, progressing 
with equal steps. That is to say, the more generalized of each 
genetic series show in their ontogeny that they were derived from 
