( 377 ) 
When interpreting these figures we must take into account that 
the average I found for five groups of adult skulls was: 44.6, 
44.7, 45.7, 46.6 and 47.9. If we compare with these figures the 
values found for the skulls of children, it is seen at once that in 
man as well as in the anthropoid apes the foramen magnum is 
shifted occipital ly during development. If the number in each group 
of infantile skulls were more numerous one would sooner feel inclined 
to draw the conclusion from the averages found that this shifting 
begins with the eighth year, about simultaneously with the changing 
of teeth. 
Having learnt how to express numerically the position and displa¬ 
cement of the foramen magnum in the Primates, we may now 
continue our investigation With the determination of the variations 
of the inclination of the plane of this aperture. This will form the 
subject of the following communication. 
Physiology. — “On the changes in the blood serum of sharks after 
bleeding .” By Mr. F. J. J. Buijtendjjk. (Communicated by 
Prof. H. Zwaardemaker). 
(Communicated in the meeting of September 25, 1909). 
The blood serum of sharks has an osmotic pressure about equal 
to that of the salt water in which they live and which varies as 
the concentration of the salts of the sea or aquarium is changed 
(Rodier l ) Botazzi 3 )). 
This osmotic pressure, measured by the lowering of the freezing 
point of the serum, is partly caused by the salts, dissolved in the 
°od liquid and for the rest by the urea which is present in high 
concentration in the body liquids of these Selachians. Schroeder s ) 
ound in the blood of Scy Ilium with large freshly caught animals 
/# urea > which figures have been confirmed by other investi¬ 
gators (Baglioni) 4 ). 
In relation with my investigations on the diuresis of sharks I put 
Myself the question whether perhaps the blood serum would after 
1] Rodier > Travaux de la Station Zoolog. Arcachon 1899 p. 108. 
^ Botazzi ’ Ergebnisse de Physiologie 1908. 
* } V ‘ Sch Roeder, Zeitschr. f. physiol. Chemie 14 p. 5 75, 1890. 
) Baglioni, Hofmeisters Beitrage 9 p. 50. 
Proceedings Royal Acad. Amsterdam. Vol. XU. 
26 
