Diphthongs ending in I, viz., EI, OI, UI, occur only in a few
interjections and in cases of contraction.

While in pronouncing the diphthong the sound of both vowels was to some
extent preserved, there are many indications that (in accordance with
the custom of making a vowel before another vowel short) the first vowel
of the diphthong was hastened over and the second received the stress.
As in modern Greek we find all diphthongs that end in _iota_ pronounced
as simple I, so in Latin there are numerous instances, before and during
the classic period, of the use of E for AE or OE, and it is to be noted
that in the latest spelling E generally prevails.

Munro says:

"In Lucilius's time the rustics said _Cecilius pretor_ for _Caecilius
praetor_; in two Samothracian inscriptions older than B.C. 1OO (the
sound of AI by that time verging to an open E), we find _muste piei_
and _muste_: in similar inscriptions [Greek: transliterated]*_mystai_
_piei_, and _mystae_: _Paeligni_ is reproduced in Strabo by
[Greek:transliterated]_Pelignoi_: Cicero, Virgil, Festus, and Servius
all alike give _caestos_ for [Greek:transliterated]_kestos_: by the
first century, perhaps sooner, E was very frequently put for AE in words
like _taeter_: we often find _teter_, _erumna_, _mestus_, _presto_ and
the like: soon inscriptions and MSS. began pertinaciously to offer AE
for E*: _praetum_, _praeces_, _quaerella_, _aegestas_ and the like, the
AE representing a short and very open E: sometimes it stands for a long
E, as often in _plaenus_, the liquid before and after making perhaps the
E more open ([Greek:transliteration]_skaenae_ is always _scaena_): and
it is from this form _plaenus_ that in Italian, contrary to the usual