54 



/ iV VER TEBRATE ZOOUHl } ' 



ming larva (Fig. 35 E) but are lost when the animal assumes the 

 adult form after becoming sessile. The tentacles are hollow, 

 usually terminating in a suckerlike knob. The macronucleus is 

 extremely variable in form. In some colonial representatives its 

 branches extend throughout the branches of the colony. A 

 micronucleus has never been demonstrated for some suctorians. 

 Binary fission, so common in the Ciliata, is rare in the suctorians. 

 Both external and internal buds are of common occurrence. The 

 embryos when liberated are furnished with bands of cilia for 

 locomotion. Conjugation, in nature similar to that found in 

 Ciliata, may take place either between 

 similar individuals or between a fixed 

 individual and a free-swimming bud, 

 suggesting the condition found in the 

 Vorticella. Podophrya, Acineta, Ephe- 

 lota (Fig. 36), Tokophrya, and Dendro- 

 soma are typical genera. 



Interrelationships of the Classes 

 OF Protozoa 



The Protozoa represent the simplest 

 present-day organization of animal life. 

 It is probable, however, that at one 

 ,^\^\ ■^?"^'^, ^"°*°".^J^ time there existed simpler living sub- 



{Ephelota biUschhana) with 



five daughter buds. (After stancc which would be Considered animal 

 Caikms). jj^ nature. This most primitive form of 



life was probably more homogeneous in 

 its make-up, for morphological differentiation of the nucleus and 

 cytoplasm and regional differentiation of the cytoplasm such as 

 we find in even the simplest Protozoa have probably resulted 

 from long periods of progressive evolution. 



There are numerous evidences that plant life existed on the 

 earth before animals came into being. The Mastigophora, 

 through the Phytomastigina, display unquestioned relationships 

 with the members of the plant kingdom (Fig. 1). Because of 

 this fact some biologists consider the Mastigophora as the most 

 primitive class of the Protozoa. 



On the other hand, the rhizopod organization is, on the whole, 

 less intricate than that of the Mastigophora or of any other proto- 

 zoan. Consequently, on the criterion of simplicity of organiza- 



