1893.] Mode of Formation of Food Vacuoles in Infusoria. 467 



stalk, and being made up o relatively transparent cell substance. 

 This animal shows such marked voracity upon occasion that I have 

 counted 100 food masses within its substance ; at the same time it is 

 only minute particles which are acceptable when offered for ingestion. 

 The shaping of the one form of matter from the other, then, promises 

 to be a process of no small interest, and actual observation has made 

 me think that it is more than merely interesting, that it may be re- 

 garded rather as the striking illustration of a process often masked in 

 other Protozoa, but fundamental in nature. 



I have fed Carcheslum with nutritious and innutritions particles, 

 with milk, with bacteria, with such flocculent precipitates as are 

 thrown down by the interaction of ditch water and alizarin sulphate 

 or congo-red, and with pigment grains carmine, Indian ink, or 

 ultramarine blue. All these are ingested readily, but the particles 

 which perhaps serve best to illustrate the striking events of diges- 

 tion are the finely-divided granules of proteid which form a precipi- 

 tate when diluted white of egg is coagulated by heat. When the 

 white of fresh eggs is treated thus, the heat precipitate is generally 

 abundant ; a very scanty coagulum may form, however, when the eggs 

 from which the diluted fluid is prepared are stale. It is known that 

 any marked alkalinity hinders effective coagulation of albumen and 

 that albumoses and peptones do appear in stale white of egg; I 

 think it fair, then, to suppose that Carchesium ingesting the abundant 

 coagulation precipitate is ingesting minute irregular fragments of 

 nutritious matter suspended in a dilute solution of salts, and that in 

 administering the merely opalescent fluid a less obvious but possibly 

 important substance is supplied soluble food. A.11 ingested particles, 

 whatever their nature, pass from the exterior by a slightly sinuous 

 ciliated pharyngeal tube which leads inwards from the wide mouth, 

 and, spacious itself at first, narrows, to end internally in a small 

 dilated sac, the oesophagus.* An anal ridge runs at right angles to 

 the long axis of the polype at the junction of the outer and middle 

 thirds of the pharynx, and from this ridge all effete matters are 

 ejected, but food particles are gathered by the oral and pharyngeal 

 cilia into the cesophageal sac, and, mixed in varying proportions with 

 the fluid medium in which the animal is living, start from its most 

 internal point on their intracellular career as a vacuole of ingestion. 



Each vacuole of ingestion thus discharged by some obscure im- 

 pulse performs a movement of progression ; it passes with a steady 

 gliding motion towards the basal attachment of the polype, coming 

 to rest at some point along the concavity of the band-like nucleus. 

 A period of quiescence follows and persists in healthy specimens for 

 some seconds, and at its end the vacuolar contents, which up to this 



* I have adopted the terminology of E. Gh-eef (' Archiv fur JXaturgesch.,' Wieg- 

 mann, vol. 37, 1871). 



