943 
n°. 15, with a length of 9 em. As a new-born monkey measures 
27 cm., that would be just a third part of the length. Now the 
third part of the length of a full term human foetus is 17 à 18 em., 
which, according to Rerzius, corresponds with the end of the 4t? month. 
When the ratios in length between the monkey embryos are 
thought similar to those which consist inter se between the human 
foetus, then with adequate development one should find the first 
indication of the origin of the fissura Sylvii, also in the embryos 
of man, only at the end of the 4» month. 
Now the records of Ecker and Rerzivs are rather similar and they 
point out the third month as the period in which the first indication 
of this sulcus is found in human embryos. This should be therefore 
a month sooner than the analogous period in Semnopithecus. 
The conclusions to which I think I may come, are therefore the 
following : 
1. The fissura Sylvii in Semnopithecus commences on the lateral 
surface, and develops towards the lateral edge, which is the reverse 
in man. 
2. The first that one sees of this fossa is a sulcus, to which 
later on, at the anterior side a second is added, both of which 
bordering the insular area temporal ‘and frontalward. 
3. The first indication of the commencement of this sulcus is 
found a month later than after the calculation in human foetus. 
4. The total operculisation of the insula is found in Semnopithecus 
at the stage which would be reached for human foetus in the 
beginning of the 6! month. 
Physiologie. — “The Olfactology of the Methylbenzol Series’. By 
Dr. E. L. Backman from Upsala (for the present at Utrecht). 
(Communicated by Prof. Dr. H. ZwWAARDEMAKER.) 
(Communicated in the meeting of January 27, 1917). 
What may be defined as an homologous series, is an arrangement 
of substances in the order of their atomicity which changes progres- 
sively and in a particular way in the same straight line. We know 
that such substances, when odorous, give a scent which also varies 
gradually and almost continuously, and evoke smell-sensations 
representing points upon an intensive scale like the atomic com- 
positions. The question whether intermediate compensations occur 
between the terms of this scale is of general importance for phy- 
siology. Hitherto the stimulus-limina of the terms of only few 
