80 ORGANIZA TION OF THE INFUSORIA. 



colouring matter of the Diatomaceae ; while in the pale and more decidedly 

 yellow examples, a nearer approximation is perhaps made to " phyco- 

 chrome," or to the yellow colouring matter of various lower algae. Among 

 the most conspicuous examples of this yellow and brown-coloured series 

 may be mentioned the majority of the Cilio-Flagellate group of the 

 Peridiniidae, and a very considerable proportion of the Tentaculifera or 

 AcinetidcTe: Similar yellow or olive pigment matter is likewise met with 

 among a large number of typical Flagellata, such as Dinobryon, Microglctia, 

 and Chrysopyxis, but is remarkable in all these types for its limitation to 

 two lateral band-like areas a circumstance which has been accepted by 

 the author as justifying their collection into the single family group here 

 distinguished by the title of the Chloromonadidae. 



As illustrations of Ciliate forms in which the colouring hue presents 

 abnormally marked features, reference may be made more especially to the 

 Leucophrys (Holophryd) sanguined of Ehrenberg, in which the parenchyma is 

 of a bright crimson colour, and Nassula ornata, in which numerous vesiculse 

 of a brilliant violet tint are found distributed throughout the same element. 

 In this latter instance, however, the colouring matter does not represent 

 an essential constituent of the body-substance, but is due to a reaction 

 of the associated juices upon the ingested food-material. An interest- 

 ing example of the occurrence of fine granular matter, differing in colour 

 from the surrounding protoplasm, is yielded by the Monas (Spumella) vivi- 

 para of Ehrenberg, in which such granules are exceedingly minute, of a 

 bright red hue, and exhibit a constant vibratory and apparently purely 

 mechanical or "Brownian" movement. Minute coloured granules of a 

 brilliant crimson hue are also found embedded in the contractile element 

 of the stem of Vorticella picta. 



Although possessing no claim for consideration as supplementary 

 colouring substance, it may be most appropriately remarked here that in 

 all of the exceedingly minute collar-bearing monads, or Choano-Flagellata, 

 a pale glaucous or fluorescent hue prevails, that assists materially in 

 the recognition of their presence, even where the magnifying power 

 employed is insufficient to render the characteristic membranous collar 

 clearly visible. A similar pale green or glaucous tint is exhibited also 

 by many species of Bacteria, and would appear to represent the predomi- 

 nating refractive index of abnormally minute protoplasmic bodies. 



Accessory Structures Trichocysts. 



First in importance among the supplementary and non-essential ele- 

 ments associated with the Infusorial economy, have to be described those 

 remarkable bodies, recurring under a variety of aspects and conditions, 

 known as " trichocysts." These structures exist in their most characteristic 

 form in the very cosmopolitan species Paramecium aurelia, taking there 

 the form of minute and exceedingly slender rod-like bodies, or fibrillae, 



