Their Collection and Investigation. 47 



are more especially subservient in both the erratic and 

 sedentary species as prehensile organs wherewith they seize 

 and transfer to their own bodies the protoplasmic contents 

 of other Infusoria. The animalcules belonging to the tenta- 

 culiferous class are not inferior to the Ciliata in regard to 

 size, and on account of their chiefly sedentary habits afford 

 peculiar facilities for systematic investigation. 



Should the microscopical investigator be so far satisfied 

 with his explorations among the ciliate and tentaculiferous 

 classes of the Infusoria as to determine upon a like study of 

 the Flagellata or monadiform animalcules, he will find his 

 path beset by more formidable obstacles, though en revanche 

 he will be entering on a new and interesting field that has up 

 to the present time been so superficially explored that he 

 may look forward with almost absolute certainty to meeting 

 with an abundant harvest of species not yet placed on record 

 in the scientific annals ; while in connection with an over- 

 whelming majority of those already known, but the scantiest 

 data have been registered concerning their life and develop- 

 mental histories. All the Flagellata are notable for their 

 minute size, a total length of the 1- 2- or 3- 1000th parts of 

 an English inch being a common measurement. They con- 

 sequently need the higher powers of the compound micro- 

 scrope — a l-8th inch objective and upwards — for then* satis- 

 factory investigation ; while even with such apparatus a 

 considerable amount of patience and manipulative skill is 

 essential for the correct definition of the number and 

 character of their diversely modified appendages. Up to 

 within a comparatively recent date the Flagellata, as a 

 clearly-defined animal group, could be scarcely said to exist, 

 its members being intermingled with the unicellular flagelli- 

 ferous Protophytes or lowest plants, and from which indeed 

 they are even yet in many instances not easily distinguished. 

 The application, nevertheless, of the standard that has been 

 selected personally as the distinction between these flagellate 

 Protozoa and Protophytes, namely, the capacity to ingest 

 solid food and the possession of a rudimentary respiratory 

 organ — the pulsating contractile vesicle — by the animals, and 



