60 THE ARRAY OF LIVING ORGANISMS 



Exercises XII and XIII 



Blue-green 

 algae 



Bacteria 



HIGHER PLANTS 



I 



Stoneworts 

 Plant- like 



flagellates 

 Green ) 

 Brown i , 

 Red °'9°«- 



GoldenI 



PROTISTS 



Lichens 



Fungi 



Slime 



molds 



I 



HIGHER ANIMALS 



I 



PROTOZOA 

 Animal-like flagellates 

 Ciliates 



(Paramecium) 

 Rhizopods 



(ameba) 

 Sporozoa 



(parasitic: 



Plasmodium 



of malaria) 



(Ancestral flagellates?) 



Each of these groups is classified at present os a distinct phylum, except that the term 

 "Protozoa" now designates o subkingdom within either the protist or animal kingdom; and 

 the flagellates as a whole constitute the Phylum Mastigophoro (whip-bearers), which includes 

 the plant- and animal-like flagellates and the dinoflagellates. 



Among the protists the bacteria and blue- 

 green algae stand somewhat apart. They are 

 highly successful groups, particularly the bac- 

 teria; yet structurally they represent the simplest 

 of living cells, and so are sometimes spoken of 

 as "lower" protists, though not ordinarily to 

 imply an ancestral position. The blue-greens, 

 like the true algae, are photosynthetic, evolving 

 oxygen in this process. The bacteria may be 

 photosynthetic or not, but never evolve oxygen 

 in photosynthesis. These two groups share the 

 following further properties: 



(1) Small size, including the smallest living 

 cells. 



(2) No separate nucleus, surrounded by a 

 membrane. 



(3) No chloroplasts. 



(4) Motionless cytoplasm. 



(5) A chemical distinction, the exclusive pos- 

 session of diaminopimelic acid.* 



The flagellates may provide the thread that 

 binds the protists together, and leads off" in the 

 directions of the multitissued plants and animals. 

 It is this that has prompted the thought of a 



flagellate ancestor, probably photosynthetic, 

 which may have given rise on the one hand, 

 with some structural retrogression, to the bac- 

 teria and blue-greens, and on the other to the 

 more highly developed protists, both plant-like 

 and animal-like. It is as though, starting with 

 an ancestral green flagellate, the photosynthetic 

 capacity had been exploited in developing the 

 algae, and the motility exploited in developing 

 such protozoa as the ciliates. 



Modern flagellates include both green, photo- 

 synthetic types (e.g., Euglena and Chlamydo- 

 nionas, both of which you have studied), and 

 colorless animal-like forms, such as the trypan- 

 osomes responsible for African sleeping sickness. 

 Flagellated cells form one stage in the develop- 

 ment of slime molds. We have also the colonial 

 green flagellates, some of which display a first 

 differentiation of function, certain cells being 

 specialized for reproduction (recall Volvox). 

 These may represent first approaches to the 

 formation of the multitissued plants. On the 

 other hand the sponges, the first of the animal 

 phyla, possess characteristic flagellated collar 

 cells that greatly resemble free-living flagellated 

 protozoa. The cells of sponges also display an 



'■ HOOC— CHNHa— (CH2):i— CHNH2— COOH, a carboxylated lysine. 



