146 



PROTOZOA 



CHAP. 



the food-vacuoles, the whole combining to present a most attrac- 

 tive picture. Ehrenberg fancied that a continuous tube joined 

 up the vacuoles, and interpreted them as so many stomachs 

 threaded, as it were, along a slender gut ; whence he named the 

 group " Polygastrica." 



Fig. 51. Carchesium 

 polypinum. Scheme 

 of the path taken by 

 the ingested food in 

 digestion and expul- 

 sion of the excreta. 

 The food enters 

 through the pharynx 

 and is transported 

 downward (small cir- 

 cles), where it is stored 

 in the concavity of 

 the sausage - shaped 

 meganucleus (the 

 latter is recognised by 

 its containing darker 

 bodies). It remains 

 here for some time at 

 rest (small crosses). 

 Then it passes upward 

 upon the other side 

 (dots) and returns to 

 the middle of the cell, 

 where it undergoes 

 solution. The excreta 

 are removed to the 

 outside, through the 

 vestibule and cell 

 mouth. The black 

 line with arrows indi- 

 cates the direction of 

 the path. (From Ver- 

 worn, after Green- 

 wood. ) 



We owe to Miss Greenwood 1 a full account of the formation 

 and changes of the food-vacuoles in Carchesium polypinum. 

 The vacuole passes steadily along the endosarc for a certain 

 time after its sudden admission into it, and then enters on a 

 phase of quiescence. A little later the contents of the vacuole 

 aggregate together in the centre of the vacuole, where they are 

 surrounded by a zone of clear liquid ; this takes place in the 

 hollow of the meganucleus, in this species horseshoe -shaped. 

 The vacuole then slowly passes on towards the peristome, lying 

 deep in the endosarc, and the fluid peripheral zone is absorbed. 



1 Phil. Trans, clxxxv. 1895, pp. 355 f. 



I 



