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rhini and Platyrrhini was almost entirely bridged over both by some 
Catarrhini and some Platyrrhini with a middling distantia inter- 
narina — was a support for his transformistical conception of the natural 
development. This was incorrect, as, I suppose, 1 have shown: the 
external nose of the monkeys of the Old World always differs from 
the nose of those of the New World. This fact can be connected 
with a supposed common descent, if we admit that in a mutation 
period of the ancestors, the two forms of the nose came into existence. 
Anatomy. — “On the Jacobson's organ of Primates”. By G. P. 
Frets. (Communicated by Prof. Dr. L. Bork). 
When examining older stages of development of some platyrrhine 
monkeys, Chrysothrix, Cebus, Ateles(?) and Mycetes I always found 
a well developed Jacobson’s organ. In some of these foetuses I 
ascertained the innervation by olfactoriusfibres. In embryos of 40 mm. 
of Macacus cynomolyus and Semnopithecus maurus no Jacobson’s organ 
is extant, but a well-developed basal cartilage, of which the Jacobson’s 
cartilage forms a part. Very young embryos of catarrhine monkeys 
have always a Jacobson’s organ. I made microscopic sections through 
the regions of the nose of two fullgrown specimens of Cebus hypoleucus. 
A well developed Jacobson’s organ was extant *) (Fig. 1). It terminates 
in the ductus nasopalatinus. A nerve-bundle (Fig. 1 2. J. 0) is in 
connection with the mucous membrane. I ascertained in series of 
older embryos, as I said before, that the nerve for the Jacobson’s 
organ belongs to the olfactorius, and consequently I am of opinion 
that I may admit, that the nerve found in the full-grown animal is 
an olfactorius-bundle. The nerve nasopalatinus of the second branch 
of the trigeminus runs through the canalis nasopalatinus and in a 
groove between the processus palatinus of the maxilla and the lateral 
part of the Jacobson’s cartilage (Fig. 1, n. np.). A lamina praeductalis 
can be distinguished at the basal cartilage — before the ductus 
nasopalatinus —, continuations of which extend to the interior and 
to the front. The continuation to the interior and medially is the 
Jacobson’s cartilage. 
Of Catarrhini I examined microscopic sections of the nasal region 
of a young Macacus rhesus and a Semnopithecus entellus. In both I 
find a well developed basal cartilage ; the Jacobson’s organ however 
is missing. In Macacus rhesus, of which I examined a hardly inter- 
rupted series, a groove separates itself on both sides of the ductus 
1) Herzreip found a Jacobson’s organ in Hapale. 
——- en 
