THE REPRODUCTIVE CYCLE 



215 



In Tjrpe 4 is represented the cycle of a simple colonial organism 

 such as the plant-like Mastigophora,^ Gonium or Pandorina (Figs. 

 104 and 105, p. 197). It will be recalled that such a colony 

 consists of a number of cells which have been formed by the 



THE CELLULAR CYCLE IN PROTOZOA AND METAZOA 



TYPES CELL DIVISION MATURATION AND SVNGAMY CELL DIVISION 



1. Simple PfOlozoan 

 Coniugal'on unknown 

 Many Flagellates 



s/ 



w-0 



2. Simple Piolozoan 



tndomuis or Aulogamy 

 Tnchomasln 



3. Simple Protozoan 



Isogamous Coniugalion 

 Aclinophrys 





Absent ? 



(^-® 



^® 







Endomuis or Autogamy 



-®-0-0-®- 



®: 





As oelore 



^®^|— ®®-5S-®- 



(^-® 

 W-0 



%4 



Fig. 110. — Cell cycles in Protozoa and Metazoa. 



division of a single cell and have remained together (c/. p. 195). 

 Such a colony is an individual of a slightly higher order than the 

 single cell of a simple non-colonial organism (Type 3), although it 

 is not truly many-celled because its cells are structurally similar 



2 The authors are sensible of the fact that these organisms, Gonium and 

 Pandorina, and also Eudorina, Pleodorina, and Volvox, are plants rather than 

 animals. The inclusion of such plant-like forms as a subdivision of the 

 Mastigophora, the Phytomastigina, has been explained (c/. p. 174). As 

 the multicellular state has probably evolved from a unicellular one along 

 parallel lines in animals and plants, the use of such plant-like organisms seems 

 justifiable for the purposes of the present illustration. 



