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back to one’s home. This paragerontic substage is not in my opi- 
nion »atavistic« or »reversionary« as it is defined by Buckman and 
Bather. Reversions are the returns or recurrence of ancestral cha- 
racteristics in genetically connected organisms which have been for a 
time latent in intermediate forms. I do not think that we can include 
in this category purely morphic characteristics which habitually recur 
in the same individual as the result of paraplasis or which occur in 
the paracme of a type more or less invariably. In the individual the 
smooth round shell of the whorl of the paragerontic substage after it 
has lost the progressive characteristic of the ephebic stage cannot be 
considered as reversions. They are simply analogies in form, not. 
structurally similar characteristics. A better known and more easily 
understood case is the resemblance of the lower jaw of the infant be- 
fore it has acquired teeth and that of the extremely old human subject 
in which these parts have been lost and the alveoli and the upper 
parts of the bony mandible have disappeared through resorption. The 
forms are similar but no one would venture to consider the infant’s 
cartilaginous jaw and that of the old man as similar in structure. 
The best examples of similar phenomena in the phylum known 
to me is the close resemblance of form between the straight Baculites 
of the Cretaceous or Jura and Orthoceras of the Paleozoic. These two 
are often confounded by those ignorant of the essential differences 
existing in their structure. One is a mesozoic straight form derived by 
degenerative processes of evolution from the highly ornamented pro- 
gressive Ammonitinae of the Mesozoic and the other is a near rela- 
tive of the primitive ancestral forms of the Nautiloids in the Paleo- 
zoic. One occurs in the paracme and the other in the early epacme 
of the group of chambered shells. They are widely distinct in their 
structural characteristics and these differences are greater in the young 
than at any subsequent stage of their ontogeny. Baculites has a close 
coiled shell in the nepionic period as has been lately demonstrated by 
Amos P. Brown of Philadelphia and Orthoceras is straight from the 
earliest stage. The return of a similar form in Baculites in the later 
periods of development in obedience to the law of the cycle does not 
carry the structure back with it to a repetition of the orthoceran 
siphuncle and sutures. 
The term used by Buckman and Bather, »Brephic« derived 
from Bpeœuxèc is perhaps etymologically preferable to nepionic but un- 
luckily it was not used in 1888. Nepionic ! has been used by authors 
on this side of the Atlantic in several essays and is found in the Cen- 
10 Originally taken from Närtos, but there is a form To vnruov. 
