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78 ORGANIZATION OF THE INFUSORIA.Colouring Matters.Under the above denomination necessarily fall those pigmentary substanceswhich in their diffused state impart, in many instances, a supplementarycharacteristic and easily recognized feature of distinction, and alsothose anteriorly located coloured corpuscles, of diverse size and number, soconspicuously represented in the families of the Euglenidae and Chloromonadidae.To these latter structures, on account of their aspect andposition, a visual function was not unnaturally attributed bythe earlierauthorities, Ehrenberg first figuring and describing them as veritable opticorgans, while at the present day they retain the title of eye-like pigmentspots.It is now, however, generally conceded that these characteristicstructures are altogether innocent of the exalted function first assignedthem, and that their true structure and composition are merely oleaginousor pigmentary, according essentially with the isolated coloured corpusclespossessed by numerous undoubted unicellular plants or Protophytes. Theunessential nature of these bodies, and the entire absence from them of allthe phenomena usually exhibited by so complex and highly organized astructure as an eye, isamply demonstrated by the exceedingly variableconditions under which they make their appearance, even among individualsof the same species. Thus, while in Euglena viridis one such characteristiceye-like pigment-spot represents the normal development, two or eventhree such corpuscles not unfrequently occur, while in yet a third seriesitmay be entirely suppressed. Although these characteristic pigmentcorpusclesare most abundantly represented among the members of theFlagellata, they occur occasionally among the Ciliate section, as prominentlyillustrated in the genus Ophryoglena, while according to Claparedeand Lachmann, such a structure is likewise present in the earlier and freeswimmingcondition of Freia (Follicularia) elegans. The Flagellate genusDistigma would seem to be the only type among the Infusoria in whichtwo pigmentary corpuscles are persistently developed, in all other forms asingle one only being normally present. Excepting in the case of Ophryoglena,in which the pigment-spot is almost black, a brilliant crimson orscarlet hue is found to predominate. No trace of these supplementarycoloured corpuscles have been yet recorded in association with therepresentatives of the Tentaculifera.Colouring matter in a diffused state, or as forming an integral elementof the entire body-substance, while not very generally developed, constitutesin certain types a conspicuous and highly characteristic feature. TheFlagellate group of the Euglenidae, distinguished for the brilliant greenhue of the entire subcuticular parenchyma, affords perhaps the most preeminentexamples of such diffuse coloration. The chlorophylloid nature ofthe pigmentary matter, or " endochrome " as itmay be appropriatelydesignated in these instances, is so evident that its presence has long been