137 
some rabbits v. Mrmaucovics 1) has tried to discover the function ; 
the animals continued to live in the same way. Here, with the 
monkeys, nature has made the experiment: Plathyrrini have a 
Jacobson’s organ, Catarrhini miss it. No communication is known 
to me that, e.g. in taking their food, Platyrrhini behave differently 
from Catarrhini. In the latter a compensation-apparatus for the 
missing Jacobson’s organ might exist. The hypothesis about the 
signification of the Jacobson’s organ, most generally defended, is that 
it might be of use as a smelling organ in the mouth by tasting 
food (vide e.g. WesrER’) p. 153). If this hypothesis were correct, 
it would be possible to indicate in Catarrhini the compensation 
apparatus. In makrosmatical mammals the regio olfactoria is separated 
from the regio respiratoria by the lamina terminalis. This is not the 
case with Catarrhini; here the cavity of the mouth is in much 
better connection with the olfactory region by means of the lamina 
terminalis, consequently a separate organ of smell communicating 
with the mouth cavity through the canales incisivi is not so much 
required, and therefore the loss of the Jacobson’s organ might 
be compensated by the disappearance of the secluded independent 
regio olfactoria. 
HERZFELD *) however communicates a fact which is very unfavoura- 
ble to the above mentioned hypothesis. According to this author 
horse, ass, giraffe, and camel possess a Jacobson’s organ, but no duc- 
tus incisivus communicating with the mouth-cavity. It is likewise 
known, that among Chiropteres the Jacobson’s organ is often missing, 
— this holds e.g. for Pteropus (HrrzreLD, ZUCKERKANDL *) — whilst 
the preparation of this animal shows that it possesses a capacious 
independent regio olfactoria. | 
In virtue of these facts I am of opinion that in the simultaneous 
disappearance of the Jacobson’s organ and the independent regio 
olfactoria in Catarrhini, and the continued existence of both in a 
reduced form in Platyrrhini, we must see a parallel phenomenon, 
an indication of the general reduction of the olfactory organ. 
1) V. v. Mrmarcovics. Anatomische Hefte. XI Band, S. 78, 1898. 
2) M. Weger. Die Siugetiere, 1904. 
3) P. HerzreLp, Zoologische Jahrbücher, 3 Bd., S. 551. 
4) E. ZUCKERKANDL. Sitzungsberichte. Wien. Bd. 117. Math. phys. Cl. 
