viii THE VOYAGE OF H.M.S. CHALLENGER. 



pen of Dr P. P. C. Hoek of the University of Leiden, I have to thank Mr 

 Darwin for suggesting to me that I should invite Dr Hoek's kind co-operation 

 in preparing the report upon the Pycnogonida, an aberrant group of Arthropoda 

 to which we had been fortunate enough to add a large number of novel and 

 striking species. Dr Hoek's memoir has proved a valuable addition to the 

 literature of the order, and I am glad to say that Dr Hoek has been induced 

 to continue his labours by monographing the Cirripedia. 



C. Wyville Thomson. 



