( 661 ) 
consequently becomes a vesicle with double parietes in the invaginated 
cavity of which the cerebral part of this organ is received. 
There was sufficient reason to accept, likewise for Tarsius, this 
very simple mode of development, as ZieneN, who has made a special 
study of the development of the brain of this primate, with specimens 
likewise belonging to the Utrecht university, does not speak of any 
deviating form of development, but points emphatically to a confor- 
mity with the usual course of development. So he says e. g. on 
page 351 of the second volume, third part of Herrwie’s Handbuch 
der Vergl. u. Experimentellen Entwicklungsgeschichte der Wirbeltiere : 
“Die charakteristische Umklammerung des Hirnteils der Hypophyse 
dureh den Rachenteil giebt die nachstehende Figur wieder.” In his 
communication, published in the reports of this Academy ') he holds 
the same view. 
My observation with regard to Tarsius suggested to me the idea 
of studying the first origin and the formation of the Hypophysis vesicle 
likewise in the other embryological specimens of Primates tbat were 
in my possession. And the result of this study was that at least 
one of the peculiarities I found in Tarsius, was elucidated. For 
it appeared to me, that the way in which the Hypophysis of 
Primates originates and develops itself corresponds almost entirely 
to that of Reptiles. An exact description of it we owe to Gaurr. 
With this group of vertebrates the vesicle does not originate in a 
single but in a triple invagination, a median and two lateral ones. 
Whereas the median invagination more specially joins the nervous 
part of the Hypophysis, the parts distinguished by Gaupp as lobuli 
laterales develop from the lateral invaginations”). It is exactly so 
with Primates. Here also what Gaver calls the ‘Vorraum’” develops 
itself first, and behind it follow the three invaginations lying beside 
each other. 
In Figure 1la—/ are represented, as a proof of this fact, a few 
sections through the origin of the Hypophysis of a young embryo of 
Macacus cynomolgus (Embr. Mus. Utrecht Selenka’s Material Embryo 
“Grethe”. The direction of the section was a little slanting. In a 
the “Vorraum” has been struck, in 4 the invagination of one of the 
lobuli laterales is to be seen, in «d the median part has placed itself 
against the infundibular-stem, and the unstringing begins, which is 
completed in e and /. I shall not enter into further details of these 
facts. | only mentioned them to comprehend more easily the form of 
the Hypophysis of Tarsius. Only this be added to the above, that 
1) These Proc. of 26 Nov. 1904. 
2) SrapeRIni afterwards observed these lobes likewise in larvae of Triton cristatus. 
43 
Proceedings Royal Acad. Amsterdam. Vol. XIII. 
