THE VOYAGE OF H.M.S. CHALLENGER. 



me had been the starting-point of my rearrangement of the entire group, — of which it is 

 one of the most conspicuous members, — so the examination I have now made, after a lapse 

 of thirty years, of the vastly greater collection of more diversified forms recently obtained, 

 has given me the opportunity of testing those conclusions by their applicability to a far 

 larger ranoe of facts. 



I. " The range of variation is so great among Foraminifeea, as to include not merely 

 the differential characters which systematists, proceeding upon the ordinary methods, have 

 accounted sjjccific, but also those upon which the greatest part of the genera of this group 

 have been founded, and even in some instances those of its orders." 



No verification of this proposition could be more complete than that afforded by the 

 discovery of the Orbitolites tenuissima just referred to. If its development were 

 arrested in its first stage, it would be taken for a young Cornuspira ; if in its 

 second, it would be ranked as a Spirolociilina ; if its third stage had been first a little 

 prolonged, and then checked, it would be recognised as a true PeneropUs ; a specimen 

 which had attained its fourth would be accepted as a true Orhmdina; and only when it 

 has entered its fifth and last does it attain that characteristic Orbitoline structure and 

 cyclical plan of growth, which are manifested in the typical Orbitolites from the very 

 commencement. Now in the Classification of M. d'Orbigny, which was in 1860 the one 

 generally followed, Cormisjnra should, in virtue of its undivided cavity, count as a 

 " Monostegue," Spiroloculina is an " Enallostegue," PeneropUs and Orhicidina are 

 " Helicostegues," and OrhitoUtes is a " Cyclostegue." That the fundamental characters 

 of four out of the seven Orders which constitute, in M. d'Orbigny's view, the primary 

 subdivisions of the group, should be thus presented by one and the same individual in 

 the successive stages of its growth, is a sufiicient proof that those assemblages cannot 

 possibly be natural; and the proof obviously applies, a fortiori, to their generic 

 subdivision ; a very marked example being presented by the relation between Orhicidina 

 and OrhitoUtes, — some advanced forms of Orhiculina abandoning the spiral for the cyclical 

 plan of growth characteristic of the Orbitoline type, whilst all, save the highest and 

 most advanced forms of OrhitoUtes, exhibit in the earlier stages of their development 

 more or less of the spiral arrangement of their chamberlets, which is the distinctive 

 characteristic of the Orbieuline type. 



II. " The ordinary notion of species as assemblages of individuals marked out from 

 each other by definite characters that have been genetically transmitted from original 

 prototypes similarly distinguished, is quite inapplicable to the group of Foraminifeea ; 

 since even if the limits of such assemblages were extended so as to include what would 

 elsewhere be accounted genera, they would still be found so intimately connected by 

 gradational links, that definite lines of demarcation could not be drawn between them." 



Not only have my own subsequent studies of this group fully confirmed me in this 

 conclusion, but I have found it accepted by every one of my fellow-workers in this 



