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1871.] 239 [Cope. 
Another mode of dental complication is by lateral repetition. Thus, 
the heel of the sectorial tooth of a Carnivore is supported by a fang along- 
side of the usual posterior support of a premolar, and is the result of a 
repetitive effort of growth force in a transverse direction. More complex 
teeth, as the tubercular molars, merely exhibit an additional lateral repe- 
tition, and sometimes additional longitudinal ones. As is well known, the 
four tubercles of the human molar commence as similar separate knobs 
on the dental papilla. 
The above are cited as examples to explain the meaning of the propo- 
sition. When fuller demonstration is desired a greater number might be 
given. 
B. ON Creu REPETITION. 
That each additional act of creation in growth was originally identical 
with one which preceded it, and therefore an exact repetition in its char- 
acter and results, is proven by the following considerations. 
It has been already determined by the study of homologies that all 
organs and parts of an organism can be referred to an original simple 
archetype. ‘ 
The question then remains as to whether the first element or lowest 
term, of a given organized part is essentially a new structure, or whether 
it be a repetition of some previously existing one. It may be asserted 
that the simplest expressions which shall cover all organs, are the solid 
segments and the hollow sack and tube. For example, we have already 
noted that the ultimate element of the limb is the first segment of the sin- 
gleray of Lepidosiren. Is this short cartilaginous cylinder (which probably 
represents the fore-limb of some undiscovered member of the Dipnoi), a 
result of the repetition of a pre-existent structural element? This is no 
doubt the case, for as will be shown beyond, cartilage, though the least cel- 
lular of all the tissues is formed originally by cell-repetition or division. 
Again, the ultimate lobules of the most complex gland are but repetitions 
of the diverticula of the simply branched, and each of the latter repetitions 
of the simple cul-de-sac, which has its origin in a convexity of an original- 
ly plane surface. This convexity is again the result of repetition of cells 
or cell-division, whereby their number is increased and the surface ren- 
dered convex. 
We are thus in both the solid segment, and hollow sack, brought down 
to cell repetition. Thus it is with organs, as with entire animals, in which, 
following the line of simplification, we reach at last forms composed of 
cells only, (Actinophrys, ¢. g.) and then the unicellular, (Amba). 
If this be the origin of organs, the question whether repetitive growth 
has constructed tissues, remains for consideration. 
In growth, each segment—and this term includes the parts of a com- 
plex whole or parts always undivided, (as the jaw of a whale or the sac- 
body of a mollusk)—is constructed, as is well known, by cell division. In 
the growing foetus the first cell divides its nucleus and then its whole out- 
line, and this process repeated millions of times produces, according to 
