SOME PROBLEMS IN THE PHYSIOLOGY OF THE PROTOZOA 305 



isolated muscle of a frog, and the question of consciousness resolves 

 itself into the query, Does the single-celled organism compare with 

 the isolated muscle or with the individual frog of which that muscle 

 forms a part ? 



In the preceding chapters it has been shown that in many forms 

 certain parts of the cell become differentiated for special functions, 

 some of which are sensory, and in the whole group of Protozoa it is 

 possible to arrange a scale of forms in which sensory differentiations 

 of the plasm become more and more complex, i.e. certain regions of 

 the cell become more irritable than others. The reactions are very 

 much the same, however, whether external stimuli be applied to the 

 least differentiated or the most complex of Protozoa. Verworn has 

 further shown ('89) that enucleated and minute parts of different 

 kinds of Protozoa also react to stimuli in exactly the same way as 

 does the entire animal, observations which confirm Gruber's earlier 

 view, that each protoplasmic element has its own " will expression " 

 ('86), and justify Verworn's assertion that each protoplasmic part is 

 the independent centre and source of its own movement, while the 

 movement of a single-celled organism is only the synchronous move- 

 ment of its many parts. Responses to stimuli are " reflex," there- 

 fore, and the conclusion forces itself that the protozoan organism has 

 no more "consciousness" than the isolated muscle of the frog. 



In addition to movement, however, other vital phenomena have 

 been cited as evidence of intelligent action. Two of the most strik- 

 ing phenomena among the Protozoa are the apparent choice of food 

 and the selection of certain materials for building the shell. Chlamy- 

 dodontidae live almost exclusively on diatoms and Oscillaria, although 

 other food is abundant ; the ciliates Enchelys, Spathidium, Chcenia, 

 Amphileptus, Lionotus, Dileplus, and Didinium feed on ciliates alone 

 (Biitschli), Actinobolus on Haltefia, while numerous other forms of. 

 ciliates may be limited in other ways, or may be omnivorous. 

 Among Mastigophora Cienkowsky ('65) observed Colpodella pugnax 

 feeding exclusively on Chlamydomonas, while the rhizopod Vampy- 

 rella spirogyrce is limited to the cells of the alga Spirogyra. Carpen- 

 ter, Romanes, and Brady ('84) all remarked upon the selective power 

 of the marine rhizopods in building their shells, and the latter in par- 

 ticular ascribed a power of intelligent action on the part of certain 

 forms, e.g. Truncatulina lobatula, which "protect themselves under 

 certain circumstances with a covering of sand." 



While these observations undoubtedly suggest willed acts on the 

 part of the Protozoa in question, there is nevertheless room for an 

 explanation along quite different, lines. It is ever necessary to bear 

 in mind, however, that all vital phenomena are exceedingly com- 

 plex, even in the simplest of forms, and any explanation, whether 



