IV THE VOYAGE OF H.M.S. CHALLENGEE. 



Medusae, SiplionophoraB, Salpse, Pteropocla, Heteropoda, Crustacea, &c., which live partly 

 at the surface of the sea and partly at various depths, and swallow large masses of Radio- 

 laria, often contain numbers of their shells well-preserved in their intestine. The ali- 

 mentary canal of Fishes and Cephalopods too, which live upon these pelagic animal 

 frequently contains considerable quantities of siliceous shells ; and another newly 

 discovered source has been found in the coprolites of the Jurassic period, which consist 

 largely of Radiolarian skeletons. 



In the investigation of this comj)licated system of organisms, I have endeavoured on 

 the one hand to give accurately the forms and dimensions of the species observed, and 

 on the other hand to present a survey of the relationships of the different genera and 

 families ; and in this I have striven especially to combine the phylogenetic aims of the 

 natural system with the essentially artificial divisions of a practical classification. Being, 

 however, a conscientious supporter of the theory of descent, I can of course lay no stress 

 upon the value of the categories, which are here distinguished as Legions, Orders, Families, 

 Genera, &c. All these artificial systematic grades I regard as of merely relative value ; 

 and from the same cause I attach no importance to the distinction of all the sj^ecies here 

 described ; many of them are probably only developmental stages, and Hke my predecessors 

 I have determined their boundaries on subjective grounds. In the systematic working 

 out of so much material one always runs the risk of doing either too much or too little 

 in the way of creating species ; but in the light of the theory of descent this danger is of 

 no consequence. 



In the carrying out of this extensive task the friendly aid of Dr. Eeinhold Teuscher 

 of Jena was of the greatest benefit to me ; at my request he was at the trouble of making 

 a large number of accurate drawings with the camera lucida, and he also undertook a long 

 series, amounting to some 8000, accurate micrometric measurements, which were of the 

 greatest value in the attempt to settle the important question of the constancy of the 

 various species ; I have alluded to this in a note at the conclusion of the Eeport (p. 1760). 

 My best thanks are due to Dr. Teuscher for the patient and careful manner in which he 

 discharged these tedious tasks. 



The figures of new species of Radiolaria (about 1600 in number) which appear in the 

 atlas of one hundred and forty plates accompanying this Report, were nearly all drawn 

 with the camera lucida, partly by Mr. Adolph GUtsch and partly by myself. The names 

 of the genera which appear at the bottom of the plates have in many cases been changed 

 since they were printed ofi", as may be seen from the explanations which accompany them. 

 Had it been possible to complete the examination of the material before the plates were 

 commenced this might have been avoided, and in many cases a better selection of figures 

 might have been made. All the drawings have been made upon the stone by the practised 

 hand of Mr. Adolph Giltsch, in his usual masterly manner, and his lithographic work, 

 which has lasted fully ten years, is the more valuable since he has himself microscopicallj'' 



