78 ORGANIZATION OF THE INFUSORIA. 



Colouring Matters. 



Under the above denomination necessarily fall those pigmentary sub- 

 stances which in their diffused state impart, in many instances, a supple- 

 mentary characteristic and easily recognized feature of distinction, and also 

 those anteriorly located coloured corpuscles, of diverse size and number, so 

 conspicuously represented in the families of the Euglenidae and Chloro- 

 monadidae. To these latter structures, on account of their aspect and 

 position, a visual function was not unnaturally attributed by the earlier 

 authorities, Ehrenberg first figuring and describing them as veritable optic 

 organs, while at the present day they retain the title of eye-like pigment- 

 spots. It is now, however, generally conceded that these characteristic 

 structures are altogether innocent of the exalted function first assigned 

 them, and that their true structure and composition are merely oleaginous 

 or pigmentary, according essentially with the isolated coloured corpuscles 

 possessed by numerous undoubted unicellular plants or Protophytes. The 

 unessential nature of these bodies, and the entire absence from them of all 

 the phenomena usually exhibited by so complex and highly organized a 

 structure as an eye, is amply demonstrated by the exceedingly variable 

 conditions under which they make their appearance, even among individuals 

 of the same species. Thus, while in Euglena viridis one such characteristic 

 eye-like pigment-spot represents the normal development, two or even 

 three such corpuscles not unfrequently occur, while in yet a third series 

 it may be entirely suppressed. Although these characteristic pigment- 

 corpuscles are most abundantly represented among the members of the 

 Flagellata, they occur occasionally among the Ciliate section, as promi- 

 nently illustrated in the genus Ophryoglena, while according to Claparede 

 and Lachmann, such a structure is likewise present in the earlier and free- 

 swimming condition of Freia (Follicularia) elegans. The Flagellate genus 

 Distigma would seem to be the only type among the Infusoria in which 

 two pigmentary corpuscles are persistently developed, in all other forms a 

 single one only being normally present. Excepting in the case of Ophryo- 

 glena, in which the pigment-spot is almost black, a brilliant crimson or 

 scarlet hue is found to predominate. No trace of these supplementary 

 coloured corpuscles have been yet recorded in association with the 

 representatives of the Tentaculifera. 



Colouring matter in a diffused state, or as forming an integral element 

 of the entire body-substance, while not very generally developed, constitutes 

 in certain types a conspicuous and highly characteristic feature. The 

 Flagellate group of the Euglenidae, distinguished for the brilliant green 

 hue of the entire subcuticular parenchyma, affords perhaps the most pre- 

 eminent examples of such diffuse coloration. The chlorophylloid nature of 

 the pigmentary matter, or " endochrome " as it may be appropriately 

 designated in these instances, is so evident that its presence has long been 



