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



what was published between the dales of the works of these authors and that of Darwin's 

 .Monographs is to be found in the above preface. Moreover, this history has met with 

 an exhaustive treatment at the hands of Prof. Gerstacker, in Bronn's Klassen mid 

 ( >rdnungen des Thierreichs. 1 The parts in which the Cirripedia are treated were published 

 in 18G9, and so we find in the German work the history of our group continued till 



about 18G7. 



Of Darwin's Monographs two (1851 and 1854) give descriptions of the living species, 

 two others (published in the same years) descriptions of the fossd ones. In the first, 

 moreover, the anatomy, embryology, &c, of the different forms find ample treatment. 

 The descriptions of the species are extremely exhaustive, each forming almost a mono- 

 graph of its own ; the discussion of the relations between the different species, and also 

 of those existing between the genera, is doubtless among the best published in this 

 department of Invertebrate Zoology. Finally, his studies, perhaps even more than those 

 of Cuvier, 2 of Martin Saint-Ange, and Burmeister, are contributions to our knowledge 

 of the anatomy of the group, and so have proved very valuable to Animal Morphology 

 in general. 



The way in which Darwin has compiled all the information scattered through 

 zoological literature has been so thoroughly exhaustive and accurate, the way in which 

 he made use of this information lias been so very critical, that his works must necessarily 

 form the. basis of all future investigations. In comparison with the immense quantity of 

 scientific information contained in his publications, but little has been added to our 

 knowledge of the group since their appearance. I propose to bring these additions 

 under three different heads : — 



1. A sketch of the development of our knowledge with regard to the number 



of the genera and species known, their geographical and bathymetrical dis- 

 tribution. 



2. A summary of what has been added to our knowledge of the anatomy, embry- 



ology, &c, of the group ; and 



3. A discussion of the different opinions published with regard to the classification 



of the group, especially since the discovery of the so-called Cirripedia 

 Suctoria or Rhizocephala. 



Under the first head I shall also refer briefly to the fossil genera and species described 

 since the publication of Darwin's Monographs. It is much to be regretted that I have 

 not been able to make the summary of the literature in this department more complete. 

 As it was an utter impossibility to go personally over the whole of zoological literature 



Gerstacker, A., Die Klassen und Ordnungen der Arthropoden wissenschaftlich dargestellt in Wort und BiLl. 

 Abtheilung 1, Crustacea, Hiilfte 1, Leipzig und Heidelberg, 1865-79 ; Rankenfussler, pp. 406-589, Taf. I.-VI. 

 2 Cuvier, G., Memoires pour servir a l'histoire naturelle et Panatomie des Mollusques, Article Anatifa, 1817. 



