715 



dispersion bands of Julius, in the neighbourhood of the simple 

 absorption line that would be observed in a gas mass at rest. If 

 however instead of one point of the photosphere we consider apart 

 of observable apparent area we only get a mean effect, which will 

 be small. 



Only a very special partition of the velocity may then give rise 

 to a strong action. 



Large velocity gradients will occur in the neighbourhood of sur- 



^ . ,dr 



laces of discontinuity; tiien / — may become very large and «even 



of another order of magnitude. Ascending and descending currents 

 may be found in neighbouring parts of space. Currents in these two 

 directions may deflect the light, so that finally the light from a 

 finite part of the photosphere may be deflected. 



The aim of this communication is only to call the attention of 

 astrophysicists to the fact, that under favourable circumstances the 

 simullaneuus existence of velocity gradients and anoiaalous dUi)evsion 

 in gases that are extremely rare and without density gradients, may 

 give rise to a dejiection of light. 



Anatomy. — ''On tin' Rehition Ijctiri'e». the Dentition of Mavsu- 

 pials and that of Reptiles and Monodelphiuns.' {First Com- 

 munication). By Prof. L. Bolk. 



(Communicated in tlie Meeting of May 29, 1915). 



On the morphological significance of the dentition of Marsupials 

 opinions have varied greatly in the course of time. The special 

 characteristic of this dentition, the almost entire absence of a teeth- 

 change, naturally gaves rise to the question : with which of the two 

 sets of teeth of the Monodelphian mammals does that of the Mar- 

 supials correspond, with the deciduous or with the permanent set ? 

 Older authors, more particularly led by comparative anatomical 

 investigations, were generally of 0[)inion that it must be considered 

 as identical with the permanent set of the Monodelphian mammals. 

 This was e.g. the opinion of Owen, Flowhr, Olufikld Thomas. With 

 the Marsupials the milk-dentition would, according to them, remain 

 undeveloped with the exception of a single tooth, namely the one 

 immediately preceding the first molar. In fact with most Marsupials 

 an existing tooth is here sooner or later expelled and replaced by 



