SECTION A. EUSTOMATA-MONOMASTIGA. 367 



the periphery. This series, ah-eady described, has received from the author the 

 self-suggestive appelhition of the Flagellata-Pantostomata. 



Among those instances in which the conclusions arrived at by Ehrenberg con- 

 cerning the presence of a true mouth have been substantiated by the results of 

 modern investigation, reference may be more especially made to the Mouas graiidis 

 and semen of the last-named authority, now included by Stein with his new generic 

 groups Cmloinonas and Raphidoinonas, and to the two important family series of 

 the Euglenidas and Chrysomonadidae as here circumscribed. Several structural, 

 functional, and developmental phenomena, in addition to those furnished by the 

 ingestive faculties, may be cited as indicative of the higher position in the organic 

 scale occupied by the Eustomatous Flagellate group now under discussion. Among 

 these it may be mentioned that the constituents of the body exhibit as a rule a 

 far more well-defined separation into external and internal sarcode layers, or 

 ectoplasm and endoplasm, than is encountered among the ordinary Pantostomata ; 

 the former element, or ectoplasm, often indeed has both the appearance 

 and all the attributes of a true cuticle. In rarer instances, again, such as Phacus, 

 Oxyrrhis, and Entosiphon, the external envelope may become so indurated 

 as to constitute a veritable cuirass as commonly met with amongst the members 

 of the higher Infusoria- Ciliata. Correlated with this firmer development of the 

 ectoplasmic or cuticular element, it is further found that the members of the 

 Eustomata rarely exhibit that plasticity and unstability of contour so generally 

 characteristic of the Pantostomata, and which manifests itself most conspicuously 

 in that order by the tendency of the animalcules to assume at will — though more 

 frequently in connection with the processes of genetic union or encystment— an 

 altogether irregular repent amoeboid phase. Concerning the developmental pheno- 

 mena of these two parallel groups, it is further worthy of note that while among the 

 Pantostomata sporular reproduction is almost invariably accompanied, as in the 

 lower Phytozoa, by the splitting up of the entire substance of the body — thus involv- 

 ing the death or extinction of the pre-existing zooid or individual — among the 

 Eustomata, as exemplified by the Euglenidae, Chrysomonadidae, and Anisonemidas, 

 such sporular bodies are more frequently developed from the endoplast alone, or 

 as entirely independent endogenous reproductive elements, the parent zooids, after 

 giving birth to these, continuing their individual existence. Phenomena of a like 

 nature, but exemplified by an exogenous mode of spore or germ production, is also 

 exhibited by Nodiluca, and is in all instances indicative of a higher grade of 

 organization than is found to obtain among the Pantostomata or other Flagellata 

 previously described. 



A tabular view of the families and genera of the Flagellata-Eustomata, as 

 defined in this volume, is herewith annexed. While, as there shown, the entire 

 series may for convenience be separated into the two sections of the Eiistomata- 

 Monomastiga and Eustomata-Dimastiga, these respective subdivisions are completely 

 bridged in the very natural family group of the Chrysomonadidae by such types as 

 Chloromonas, Chrysomonas, and Microglena. 



Section A . E U STOMA TA-MONOMASTIGA 



(Flagellum single). 



Fam. I. PARAMONADIDiE, S. K. 



Animalcules entirely free-swimming, more or less persistent in form, 



bearing a single terminal flagellum ; endoplasm transparent, colourless, 



more or less granular ; oral aperture distinct, situated near the base of the 



flagellum. 



The presence of a distinct oral aperture alone distinguishes the representatives 

 of this family from those of the Pantostomatous group of the Monadidae previously 



