680 GEOFFREY LAPAGE 



least a sign of vitality, some attention was paid to the time of 

 their appearance, their numl)er, and their rate of pulsation. 



A series of observations upon many extruded spheres estab- 

 lished the fact that th(* contractile vacuoles appeannl in them 

 at irregular int(<rvals after their extrusion. In one case, 

 for example, a contractile vacuole appeared in the extruded 

 sphere in less than a minute after its extrusion, and one minute 

 after extrusion, two contractile vacuoles were present. In 

 another case, however, no change occurred in the extruded 

 sphere until twenty-two hours had elapsed, when two con- 

 tractile vacuoles appeared. But in the majority of cases one 

 contractile vacuole had appeared in anything up to twenty 

 minutes after extrusion and two were present about half an 

 hour later. The number thereupon generally increased to 

 four, or in a few cases to six or even eight. 



It would be natural to assume that the appearance of several 

 contractile vacuoles in the sphere was an exceptional occur- 

 rence, perhaps indicating a pathological condition of the 

 sphere itself or unfavourable physical conditions of the fluid 

 in which it lay. The active amoebae in the same fluid also con- 

 tained more than one contractile vacuole. Indeed, according 

 to Penard (21), Amoeba vespertilio often possesses two 

 or three. In my cultures some amoebae were certainly seen 

 with only one and others with several, so that no accurate 

 statement can be made as to what is the normal number. 

 But, if the amoebae in the hanging drop contained more 

 than one, it was not remarkable that the spheres should also 

 develop several, when they were extruded into the same 

 chemical and physical environment. 



It was, however, noted that the numbers of contractile 

 vacuoles in any particular sphere might change. In spheres 

 which contained four or more this number was often reduced 

 to two, especially in those spheres which, as we shall see below, 

 developed pseudopodia and moved away. The observations 

 on this point were not, however, sufficiently numerous to bear 

 more than the suggestion that the development of numerous 

 contractile vacuoles in the sphere was a temporary reaction 

 to its sudden change of environment, which disappeared as 



