lNTROIM'CTION 



Subscribers arc now receiving the supplement to the sixth issue. 



Since two years now elapse between the appearance of two successive full 

 issues, it has become more difficult to trace the addresses of collaborators who 

 have moved in the meantime. It is therefore desirable that everybody keep us 

 informed about any changes of address. 



This supplement is free of charge. We hope to be able to maintain the 

 rule of a cost-free supplement also in the future without increase of the 

 subscription price. 



For Dractical reasons it is impossible to repeat data of the "Supply and 

 Demand Service" from previous issues, when no new information has been 

 received. Since with every new list all previous lists become invalid, this means 

 that it is desirable that all Institutes interested in he Service send in 

 their data every year. If there are no changes, it is sufficient to 

 send a statement that the information is still valid. 



This year for the first time data have reached us from the U.S.S.R., viz. from 

 the A. N. Severtzov Institute of Animal Morphology at Moscow. With a view 

 to keeping our information up to date we have, by way of exception, included 

 the names with the subjects in the list of addresses, and have listed the 

 staff separately on page 7. 



P. D. NIEUWKOOP. 



