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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 m 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 



