THE FLAGELLATA 



197 



Whereas it is at the best doubtful whether Euglena ever 

 ingests solid particles as food, there is no doubt that the 

 nutrition of Copromonas is holozoic and that the cytostome 

 is a true cell-mouth. All sorts of bacilli, micrococci and other 

 organic particles are drawn into it, and pass down the cyto- 

 pharynx, but only the smaller particles are taken into the 

 protoplasm at the hinder end of the latter structure; the 

 larger bacilli and bacteria are rejected and returned to the 

 exterior through the cytostome. The minute particles that are 

 ingested at first lie in the protoplasm at the bottom of the cyto- 

 pharynx without any vacuole surrounding them, but presently 

 they become agglutinated into balls and surrounded by food 

 vacuoles. In this condition they are aggregated in the hinder 

 part of the body and slowly digested. The progressive stages 

 of digestion are indicated by the different colour reactions given 

 by such an inlra vitam staining reagent as neutral red. 



The nucleus lies in the posterior half of the body, and is 

 not connected in any way with the flagellum as is often the 

 case in Flagellata. In stained specimens it is seen to consist 

 of a central deeply staining mass surrounded by a clear non- 

 stainable zone, which in turn is bounded by the nuclear 

 membrane. The central mass seems to consist of an achro- 

 matic substance containing variously sized granules of 

 chromatin, and achromatic threads radiate across the clear 

 zone, connecting the central body with the nuclear membrane. 



The monads whose structure and habits have just been 

 considered may be observed to multiply rapidly by longi- 

 tudinal division for some four or five days of their existence 

 in the medium in which they are cultivated. Towards the 

 end of this time but no definite time limit can be assigned, 

 for the period is apparently very variable a number of them 

 are found to be conjugating in pairs, and for the next three 

 or four days conjugating couples are more numerous than 

 individuals undergoing division. Many of the zygotes re- 

 sulting from conjugation become encysted and pass into a 

 resting condition, but others continue to lead an active life 

 and reproduce themselves asexually by division. Hence it is 

 clear that the whole life cycle of Copromonas is divisible into 

 two periods, the one asexual and the other sexual. In fig. 42 

 the asexual period is represented by the upper circle, the 

 sexual period by the lower circle. 



