Nature and affinities 79 



The animal organism, on the other hand, has to take in from the outside 

 elaborated materials insoluble in water, and for the necessary enzyme-action 

 to work efficiently during the assimilation of these substances, they must be 

 confined within a space which is more or less limited. Consequently, the 

 normal animal organism has had perforce to adopt a method of ingestion 

 of solid food-substances. This type of nutrition is holozoic. 



Other methods of nutrition have arisen by modifications of the holo- 

 phytic or holozoic types. The saprophytic Peridiniese are probably mostly 

 degenerate forms. 



The ancient idea that the power of independent locomotion was the chief 

 criterion of the animal nature of an organism has had to be entirely dis- 

 carded in the light of modern knowledge 1 . It was this belief which for so 

 long stood in the way of the full and proper investigation of the various 

 groups of Flagellates. 



The Peridiniese are particularly interesting for the reason that in a few 

 forms it seems probable that there has not been that complete divorce 

 between the holophytic and holozoic methods of nutrition which is as a rule 

 evident at the very inception of an evolutionary series. 



There are a few observations, most of them rather old, on the ingestion 

 of solid food by certain of the Peridiniese by means of pseudopodia extruded 

 from the protoplast ; and there is good evidence that one or two members of 

 the Gymnodiniacese, the most primitive group of the Peridiniese, become 

 amoeboid in one stage of their life-history and take in solid food-particles. 

 Should these observations receive further confirmation they must be regarded 

 as actual facts, and their explanation is fairly clear. The action of the 

 environmental influences on the Flagellates from which the more primitive 

 Peridiniese were evolved, was at first insufficient to bring about the complete 

 inhibition of whatever tendencies these organisms possessed towards holozoic 

 nutrition. Thus, there are a few examples within the Peridiniese of holo- 

 phytic, or degenerate saprophytic, organisms which for a brief period, either 

 spasmodically or at some definite stage in their life-history, assume a holozoic 

 method of nutrition. 



The occurrence of trichocysts in several widely different forms of the 

 Gymnodiniacese and Peridiniacese, and especially the presence of nematocysts 

 in Polykrikos, is yet a further proof that the animal attributes were not 

 completely eliminated during the evolution of the Dinoflagellates. 



The affinities of the Peridiniese are somewhat obscure, but that the group 

 is not far in advance of certain sections of the Flagellata is fairly certain, and 

 it may be that they originated far back among the free-swimming Cryptomo- 

 nadinese as suggested by Pascher ('11). There really seems to be every 



1 Consult footnote on p. 162. 



