INTRODUCTION 25 



in the least, animal forms being derived from plants in a polyphyletic 

 series, he does not hesitate to rank certain of the fungi, together 

 with the Sporozoa and bacteria, as animal forms; the majority of 

 chlorophyl-bearing Protozoa, on the other hand, are placed with the 

 plants. 



Another differential, which, perhaps, has been the most widely 

 accepted, is the power of spontaneous motion. It is supported to-day 



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Fig. 9. — A sphseroidal colony, Uroglena americana Caikins, consisting of monads embed- 

 ded in a gelatinous matrix. 



as the most universal of the arbitrary differentials by Butschli, Bergh, 

 and Delage. Briefly stated, all forms, which are freely-motile 

 in their adult life, are animals, while stationary forms are plants. 

 This distinction is applied only to the lower forms, and not to the 

 higher groups, but even as thus limited, this differential would neces- 

 sitate some striking changes in existing schemes of classification. 

 The freely-moving diatoms, which, since the time of Nitsch ('38) 

 have been classed with the unicellular plants, would be included 

 among the Protozoa, while the majority of Sporozoa, which are almost 

 devoid of motion, would be excluded. 



The point of view which demands the strict separation of animals 

 and plants has, however, little utility save perhaps to determine the 

 limits of a text-book or monograph. Many observers, recognizing this 

 truth, have included all forms in which the transition from plants to 

 animals is shown, in a special group of the Protozoa, and usually with 

 some heading which gives a clue to their position. This is first seen 

 in Aristotle's Zodphyta (Ccelenterata) ; again in a more modern form 

 in Perty's Phytomastigoda, and in the Phytoflagellida of Delage. 

 Haeckel ('66) made a group of equivocal forms large enough to include 

 all of the Protozoa, and, under the name Protista, vainly attempted 

 to establish a third kingdom between the animal and the plant. 



