II 



PHYLUM PROTOZOA 



103 



and the consequent assumption of a more definite form of body 

 than can possibly be produced by the flowing protoplasm of a 

 Foraminifer or a Radiolarian. On the other hand, the nucleus 

 of the Radiolaria is a far more complex structure than that of 

 the Mast rgophora:. and in Foraminifera, Radiolaria, and Heliozoa 

 the organism frequently begins life as a flagellula, a fact which, 

 on the hypothesis that the development of the individual recapitu- 

 lates that of the race, appears to indicate that these orders of 

 Rhizopoda are a more recently developed stock than at any rate 

 the lower Flagellata. These circumstances, and the fact that 

 Mastigamoeba might equally well be classed as a lobose Rhizopod 

 with a flagellum or as a Flagellate with pseudopods, seem to 

 indicate that the actual starting-point of the Protozoa was a form 



Radiolaria 

 Foraminifera 



Lobosa 



Mycetozoa 



Dinoflagellata 



Cystoflagellata 



Heliozoa Choano . 

 Flagellata 



Tentaculifera 



Ciliata 



Flagellata 



Sporozoa 



FIG. 77. 'Diagram showing the mutual relationships of the chief groups of Protozoa. 



capable of assuming either the amoeboid or the flagellate phase. 

 From such a starting-point the Lobosa, Foraminifera, Heliozoa, 

 Radiolaria, and Flagellata diverge in different directions, the first 

 four keeping mainly to the amoeboid form, but assuming the 

 flagellate form in the young condition, in the case of Foraminifera, 

 Heliozoa, and Radiolaria. 



The Choanoflagellata, Dinoflagellata, and Cystoflagellata are 

 obviously special developments of the Flagellate type along 

 diverging lines. 



As to the Ciliata, Midticilia and Lopliomcnas (Fig. 71,1% and 13) 

 appear to indicate the derivation of the order from the Flagellate 

 type, since their cilia are long and flageilum-like ; but the evidence 

 is not strong and no other is at hand. The derivation of the Tenta- 

 culifera from a ciliate type appears to be clear. The Tentaculifera 

 and the hypotrichous Ciliata are undoubtedly the highest develop- 



