164 COMPARATIVE ANATOMY 



from which the chromatophors radiate can be seen to have 

 increased in size. On the other hand, if Euglense are kept in 

 the dark the granules diminish. These granules consist of 

 paramylum, and they are arranged round a central corpuscle 

 of rather dense proteid material, which is considered to be 

 equivalent to the proteid structures found in many Flagellata, 

 and known as pyrenoids. True pyrenoids are found in only 

 a few of the green Euglenoids, and when present they are 

 always closely associated with the chromatophors. For every 

 chromatophor there is a single pyrenoid, projecting from its 

 surface, and consisting of a central proteid mass surrounded 

 by a sheath of paramylum. In other Flagellates the sheath 

 consists of true starch. It should be noted with respect to 

 both chromatophors and pyrenoids, that these minute com- 

 ponents of cell structure behave in certain respects like cells 

 themselves. They never arise independently, but always as a 

 result of the division of pre-existing bodies of the same nature ; 

 pyrenoid arising from pyrenoid, and chromatophor from 

 chromatophor. Hence there are authors who would carry 

 Virchow's aphorism still farther (see p. in), and would say not 

 only "omnis cellula e cellula," but also "omne granulum e 

 granule " ; a generalisation true enough for the bodies we 

 have just been considering, but not yet applicable to all the 

 kinds of granules found in cells. 



From what precedes it is obvious that in its nutrition 

 Euglena differs from animals in general, and resembles the 

 vast majority of plants. The question is whether its plant- 

 like, or, as it is called, holophytic, mode of nutrition is supple- 

 mented by the true animal mode of ingesting solid food, called 

 holozoic nutrition ? It has been asserted that the action of the 

 flagellum causes a vortex in the small conical depression from 

 which it springs, and that minute particles of solid matter, 

 swept in by the vortex, are ingested by the Euglena and serve 

 as food. Hence the opening has been styled a mouth, the 

 depression a gullet. But, as a matter of fact, there is but one 

 well authenticated instance of the ingestion of solid food by a 

 green Flagellate, and that not by a Euglenoid, but by a species 

 known as Chrysomonas flavicans. On the other hand, it would 

 seem that in Euglenae the holophytic nutrition is supplemented 

 by another mode known as saprophytic. It has been observed 

 that Euglena will live and apparently flourish in complete 



