Proceedings of the section of sciences - DWC - KNAW

- 289 -
( 787 J
mg to my view more complicated tban would have been the case
according to the two above mentioned excalation theories. Two phenomena
may be distinguished in this process of development, namely
progressive development of one of the elements: 1I2 3 10ses Hs character
of temporary element and becomes persistent, and the second phenomenon
is the reduction of two other elements. These two elements
are at the extl'emity of each of the two tooth series) P8 at the end
of the series of replacing teeth, M3 of the end of the series of
(he teeth of the first generation. Oontrary to the two above mentioned
excalation hypotheses 1 might clistinguish the one defencled by me
as the hypothesis of the terminal reduction. I sha11 try to show
the correctness of my opinion.
If I let ma of the Platyrrhines become a persistent tooth, no
new principle is introduced into odontologie. For It is kwown to us
from otbel' groups of animals that milk teeth may become persistent
teeth; I remind the reader of the lVIarsupiaJia, where but tor some
exceptions the whole set of milk teeih has become a set of persistent
teeih except a single looth. Furthermore to Erinacaells, where according
to the investigations of LEeR!!: the sa called persistent set of teeth
consists partly of mille teeth partly of permanent teeth: 80 my
opinion is nothing more (han a. new example of the tendency a1so
observed e1se,vhere of a diphyodont set of teeth to pass into a
monophyodont. 80 against the principle as snch there ean be no
objection.
As a first argument fol' the correctness of my opinion I state the
morphology of tIle mille 11101a1's in platYl'l'hiues, I had the opportunity
of stndying them from Hapale, Ohrysothrix, Oebus, Mycetes, Pithecia
and Ateles. Without going into details it must only be mentioned here
_ that m'3 of the platyrrhines clifIers a great deal both in the composition
of its crown and jn the l1umber of its t"angs from ?n 1 or 177"
allel shows much resemblance to 'trIl of these apes.
lt is of much imporiance with this that '/11 3 is fnnctionally a
lligher developed tooth th all its decidllons tooth Pa, sa that means
that at the moment that ma ió replaced by P 3 ) the set of teeth
becomes to a certain degree fllJlctionally inferiol'. So jf ?na becomes
persistent, this means a gain for the mechanism of the set of teetl1.
This does not hold tl'ne fol' 1)/,1 anel ?n 2 , ihe l'eplacing P1 and P 2
are fnnctionally higher developed.
A second motive is derived from the development .of the set of
teeth of ihe catanhine Primates, in parLiclllar thai of man. So accol'ding
to my opinion our firs! molar has passed from a mille tooth into
. a persistent tooth in a l'elatively recent stadium, with the PlatJ:1'-