8 



Gregarinida may have diverged from the other Protozoa at a 

 point close to this form, or one of the other allied Monera. 

 On the other hand, it is possible that the Gregarinida may 

 have degenerated from one of the higher Protozoa — from 

 some form above Amoeba — or even from still higher animals. 

 The dotted line in the table, stretching downwards from the 

 base of the Metazoa, may serve to recall the possibility that 

 the Gregarinida are a much degraded offshoot from some 

 group of Gastrea-like organisms. 



The two remaining large groups of the Protozoa — the 

 Foraminifera and the Radiolaria — may be satisfactorily traced 

 back to ancestors which must have been closely allied to 

 Amoeba. As it is improbable that Amoeba has remained 

 absolutely unchanged since the time when the Foraminifera 

 and Radiolaria diverged, it has been placed in the table not 

 on the main line but upon a short side branch considerably 

 above the Monera. The ancestral forms which occupy the 

 axis between Protomyxa and the point nearest to Amoeba 

 must have gradually acquired a well-marked endoplast, while 

 at the same time, the protoplasm became more and more 

 differentiated into two layers, the ectosarc and endosarc, in 

 the former of which a contractile vacuole * was developed. 

 It is possible that the AmoebidaB, the Foraminifera, and the 

 Radiolaria may all have had a common ancestor from which 

 the three lines started. 



Taking the Foraminifera first, we can trace their origin 

 from the Amceba-like form on the main stem through the 

 ancestral Lobosa. The stages by which a shell of some kind 



* PosBibly this structure was not present in the ancestral forms, and has 

 been acquired since by Amoeba, Actinosphcerium, &c. I think that the 

 contractile vacuole in the higher Infusoria must be regarded as having been 

 evolved independently in that group. The only alternative is to place the 

 point of origin of the Infusoria much higher up on the main axis, above an 

 ancestral form possessing a contractile vacuole, and to consider the lower 

 Infusoria as degraded forms. 



