VIII.] THE PROTEUS ANIMALCULE. 371 



different constitution from the rest, so that it acquires a 

 certain appearance of distinctness when it is acted upon 

 by such reagents as acetic acid or iodine, or when the 

 animal is killed by raising the temperature to 45 C. 

 Physically, the ectosarc might be compared to the wall 

 of a soap bubble, which, though fluid, has a certain vis- 

 cosity, which not only enables its particles to hold together 

 and form a continuous sheet, but permits a rod to be passed 

 into or through the bubble without bursting it ; the walls 

 closing together, and recovering their continuity, as soon as 

 the rod is drawn away. 



It is this property of the ectosarc of the Amoeba which 

 enables us to understand the way in which these animals 

 take in and throw out again solid matter, though they have 

 neither mouth, anus, nor alimentary canal. The solid body 

 passes through the ectosarc, which immediately closes up 

 and repairs the rent formed by its passage. In this manner, 

 the Ama>bcz take in the small, usually vegetable, organisms, 

 which serve them for food, and subsequently get rid of the 

 undigested solid parts. 



Ingested matter is invariably taken in, in conjunction 

 with a watery vacuole of ingestion such as has been de- 

 scribed for Vorticella (pp. 361 2). If the matters thus 

 introduced be nutritive and digestible the vacuole persists, 

 during at any rate the earlier stages of digestion ; later, the 

 unassimilable innutritious portions of the same are cast out 

 surrounded by a vacuole of egestion. Experiment has led 

 to the belief that Am&bce will not digest fat globules or 

 starch grains. In the case of the latter the grains have 

 been seen to be thrown out 6 7 days after ingestion, 

 unchanged in their optical characters and in their behaviour 

 towards certain reagents and unaccompanied by the vesicle 

 of egestion. 



24 2 



