ii] HABITS OF CONVOLUTA 57 



theless, by exploiting their background reaction, they 

 may be picked out easily. 



By laying a small sheet of white paper on a black 

 cloth and standing the dish containing the animals 

 partly on the black and partly on the white ground, 

 the animals are caused to accumulate above the 

 latter. There, however, they are almost invisible ; 

 but by turning the vessel round so that the part 

 above the white paper is brought over the black 

 cloth, the animals may be seen distinctly and picked 

 out by means of a fine pipette before they scuttle 

 oif again to the white ground. To transfer a young 

 C. roscoffensis from one vessel to another is difficult 

 enough till its geotropism is pressed into service, when 

 the operation becomes quite easy. The animal is lifted 

 in a pipette ; but on endeavouring to expel it from the 

 tube by pressing the indiarubber nipple of the pipette, 

 only the water is discharged, and C. roscoffensis is left 

 sticking to the side of the glass tube. To avoid this, the 

 pipette is held vertically and no effort made to eject the 

 water. The slight, involuntary shaking of the hand 

 suffices to render the animal negatively geotropic. 

 Down it swims till it reaches the drop of water at the 

 point of the pipette, whence the gentlest pressure 

 suffices to transfer both drop and animal to another 

 vessel. 



So far, this study of the behaviour of our plant- 

 animals has been confined to the investigation of their 



