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Prof. A. B. Macallum. Acineta tuberosa : [Feb. 19, 



the hillock, which layer, in other Protozoa, answers to what is known as the 

 ectosarc. 



The axial portion of the tentacles is constituted of the ordinary cytoplasm 

 of the organism. It is almost homogeneous in composition, or hyaline in 

 appearance. The material composing it does not appear to be derived 

 from the cytoplasm of the hillock, but from that at a considerable distance 

 below the hillock. This is clearly shown in fig. 2, in which are represented 

 the channels in the cytoplasm, along which flows the more fluid and very 

 finely granular material constituting the axial portions of the tentacles. 



The currently accepted view as to the action of these tentacles in the 

 absorption of food is that they are hollow and are provided at their ends with 

 a cup-like sucking organ through which the food enters and is carried by 

 suction action into the cytoplasm. The existence of a cup-like terminal for 

 each tentacle I am unable to establish. There is nothing to suggest the 

 occurrence of such a structure. The structure of the capitate point is that 

 represented in fig. 7. As is not infrequently the case, the surface film of the 

 point may be deeply impregnated with fatty substance which is sharply 

 demonstrated in formol-scarlet-red preparations, but lipoid material is found 

 in droplets irregularly at other points in the film along the course of the 

 tentacles. 



The tentacles are not always straight. They may exhibit a slight or a 

 marked curve, but, as a rule, only one, or at most several, in a group, are so 

 affected. When the tentacles are being retracted they become straight and 

 the capitate end of each is reduced in diameter until the latter equals the 

 transverse diameter of the tentacle itself, which does not decrease, however 

 much the longitudinal diameter may diminish. The retraction affects all the 

 tentacles in the two groups on a form equally, and it may proceed until, 

 finally, they are but slight prominences on the external surface of the hillocks. 

 It is, indeed, very rare to find them completely withdrawn into the hillocks. 



From all the phenomena involved in the extension and retraction of these 

 tentacles it is to be inferred that alterations in surface tension are involved. 

 These alterations may affect different portions of the surface of the organism. 

 The protrusion of the tentacles may be due to an increase of the tension of 

 the general surface while the tension of the film at the points where the 

 tentacles originate may remain as before, or the tension of the general surface 

 may be constant while the tension of the film at the points where the 

 tentacles develop may diminish. There is the possibility also that, while the 

 tension of the general surface may increase, that of the film at the points of 

 origin of the tentacles may decrease. 



Whether, however, the tension of the surface film over the general surface 



