458 NATURE AND MAN. 



would here seem to be excluded by the fact that the whole series 

 of ancestral forms through which the most elaborately constructed 

 Orbitolite now existing may be assumed to have passed, continue 

 to live and flourish at the present time. The very same dredging 

 may bring up shells of Cormispira, constructed upon the undivided 

 spiral plan shown in Fig. V., i ; shells of Spiroloculina, in which 

 the spiral is partially interrupted by rudimentary partitions, as at 

 2 ; shells of Peneroplis, in which the partitions are complete, bu 

 traversed by pores, as at 3 ; shells of Orbiculina, in which the 

 peneropline chambers are divided into chamberlets, the plan 

 of growth still remaining spiral, as at 4 ; and shells of the three 

 types of cyclically growing Orbitolites 5, 6, 7. As already 

 stated, the condition of the sarcodic body undergoes no corre- 

 sponding advance \ that of the most " complex " Orbitolite being as 

 homogeneous or undifferentiated as that of the simple Cornuspira. 

 There is no evidence whatever of any " struggle for existence " or 

 " survival of the fittest " ; all showing themselves equally fit to 

 survive. All " variation " seems to have taken place in such a 

 definite direction, as to evolve calcareous fabrics of ever-increasing 

 complexity ; but this complexity can scarcely give any advantage 

 to the organisms which have attained it, these being fully as 

 incapable as the simpler forms of escaping from their enemies by 

 movement, and showing no such differences of aspect as would 

 enable them to elude observation. In fact, the Fishes and larger 

 Crustaceans which would probably be their chief destroyers, would 

 be likely to be most attracted by the larger disks of the " com- 

 plex" type; while the younger specimens of that type, being 

 indistinguishable except by the Microscopist from full-grown 

 specimens of the "simple" and " duplex" types, are not likely to 

 be passed over by any hungry destroyer that might find these latter 

 of more suitable dimensions. 



The last remark I have to make in relation to this noteworthy 

 " instance," is that its value is not in the least degree lessened 

 by the fact that the evolutionary process seems to be dependent 

 upon physical agencies. The Orbitolite type (as at present known 

 to us) flourishes best in tropical or sub-tropical seas ; the largest 

 " complex " forms yet discovered being found on the Fiji reefs ; 

 while the smallest " simple " forms only extend as far north as 



