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that here, also, as in the omission of characters in the earlier stages of 
ontogeny, the heritage is incomplete. 
Of the complications of inheritance that arise from larval adapta- 
tions, intra-uterine adaptations, and special adaptations arising in later 
life, I shall not speak. All of these have been repeatedly discussed (see 
for example Smith 57), and are well understood. gainst all of these 
the paleobiologist must be on his guard. All of these factors tend to make 
the parallelism between ontogeny and phylogeny inexact, as long ago 
pointed out by Cope (15). Yet in spite of the operation of these factors, 
the cases in which there is clear evidence of recapitulation are so numer- 
ous, and so well known to the paleobiologist, that were it not for the 
continually reiterated statements of certain embryologists that there is 
no such thing as recapitulation, I should hesitate to again point them 
out. I shall now take up the evidence according to the groups of or- 
ganisms in which it has been ascertained; and I once more remind the 
reader that most of this evidence applies to the epembryonic and not to 
the embryonic stages. 
le 
Cephalopoda.—lle only existing representative of the great group 
ot Tetrabranchiata, the class to which nearly all of the fossil cephalopods 
belong, is the Nautilus. The genus Nautilus is a striking example of the 
persistence of a primitive type. It belongs to the more primitive branch 
of the tetrabranchs, from which, according to all the evidence, the marvel- 
ously complex ammonities, on the one hand, and the modern naked cepha- 
lopods are descended. Nautilus is the only tetrabranch of which the 
entire ontogeny, including the embryonic stages, is known. 
This lack, however, in the case of the fossil genera is not as serious 
as might be supposed, for the reason that even in these ancient forms all 
of the growth stages from the latest embryonic (phylembryonic) stage to 
the adult are preserved in every complete individual shell. An inspection 
of the Nautilus shell makes this at once apparent, for the earlier stages 
of the shell are surrounded and protected by the later, and no part of 
the shell is lost or resorbed. In the straight and loosely coiled shells 
only, such for example as Orthoceras, Cyrtoceras, etc., is the case different ; 
and even here, barring injury, or the dehiscence of the earlier chambers, 
every post-embryonic stage is preserved. From a study, therefore, of a 
single shell, we are able to make out perfectly all of the epembryonic de- 
