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



its clear demonstration of the close affinity between OrhitoUtes and Orhkxdina, whereby, 

 as the place of the latter in the group Fokaminifera was beyond all question, that of 

 the former also was assured, — the Bryozoic doctrine of EhrenlxTg being thus altogether 

 •disposed of. And it followed, as a corollary, that any classification of Foraminifera must 

 be based on wrong principles, which ranked two organisms so essentially similar as 

 OrhitoUtes and Orhiculina in different Orders. 



Having afterwards come into possession, by the kindness of Mr. Jukes, Mr. Hugh 

 €uming. Prof. E. Forbes, Prof. J. Quekett, and other friends, of a large series of 

 ■different t}^3es of Orbitoline structure, obtained from different localities, including several 

 very perfect specimens w^hich had been taken alive and preserved in spirit, I applied 

 myself afresh to the study of the genus ; and soon found it to have a most important 

 bearing on the great question of the " Range of Variation within the Limits of Species," 

 w^hich was occuppng the attention of some of the most thoughtful Naturalists of that date 

 {1850-56), before the appearance of the new light thrown upon it by the publication of 

 the Origin of Species. And in 1855 I presented to the Royal Society a Monograph 

 of the genus OrhitoUtes (Phil. Trans., 1856, p. 181), in which I treated all its forms 

 — fossil as weU as recent — that I had been able to examine as varieties of one 

 fundamental t)rpe, incapable of being ranged under specific definitions, because of the 

 gradational transition clearly traceable throughout the entii'e series, from the smallest and 

 simplest OrhitoUtes marginaUs to the largest and most complex OrhitoUtes complanata, — 

 this transition showing itself alike in the progressive complication of the general structure, 

 and in the exchange of the spiral plan of growth for the cyclical. 



My subsequent studies of other types of Foraminifeka gave me a clearer insight into 

 the place of OrhitoUtes in the series : and in the concluding summary appended to my 

 fourth Memoir (Phil. Trans., 1860, p. 571), I showed how completely the results of 

 my researches were opposed to the principles on w-hich the classification of M. d'Orbigny 

 had been framed ; and sketched-out the line of " descent with modification," by which a 

 division of the primary segments that form the simply-chambered shcU of a Penerophs 

 into sub-segments, would give origin to the spiral Orhiculina, while the transition 

 from the latter to the perfectly cyclical OrhitoUtes is quite gradational. 



AVhen I subsequently undertook, in conjunction with my friends W. K, Parker and 

 T. Rupert Jones, to frame an entirely new classification of Foraminifera on the basis of 

 the principles I had laid down, I felt no difficulty in assenting to their view that the 

 pedigree of this series might be traced yet further back, viz. , to those simplest forms of 

 the Milioline type whose shell is a flattened nautiloid spire, altogether destitute of 

 partitions, belonging to that " monothalamous " section w^hich all pre\dous systematists 

 had ranked as fundamentally distinct from the " polythalamous." " From the undivided 

 spiral of Cornuspira " (I pointed out in my Introduction to the Study of the Foraminifera, 

 p. 67) " to the regular scarcely-divided spiral of certain Spiroloculine forms of MiUola, 



