On suction in Suctoria 



disappear the body was considerably larger, as seen in profile, than it had been 

 originally. Although again it might be suggested that the wrinkling was due in part 

 to a loss of material to the shrunken Paramecium, there is no positive support for this 

 view, and there is no doubt that the body surface expanded. It seems likely that the 

 attachment of the tentacles to the prey activates the suctorian to an expansion of the 

 body surface which makes room for the uptake of food. 



EFFECTS OF HIGH HYDROSTATIC PRESSURE 



The interpretation of the expansion of the body surface has been carried a stage 

 further by a study of the effects of high hydrostatic pressure (Kitching, 1954). 

 Experiments have been carried out with pressures ranging up to 15,000 lb. per sq. 

 inch (1,020 atm.). At pressures of 2,000 lb. persq. inch (136 atm.) and over, the body 

 surface wrinkled. This wrinkling developed in from half a minute to one minute at 

 the lower pressures, but took place within a few seconds at the higher pressures. 

 There was also a tendency for the cuticle to separate from the underlying proto- 

 plasm, and for the protoplasmic surface to become rounded within the cuticle. At 

 the higher pressures this happened at the same time as the wrinkling, but at the 

 lower pressures it was often delayed, and did not always occur. At a pressure of 

 2,000 lb. per sq. inch (136 atm.) the body surface often became smooth again even 

 while the pressure was still maintained, but at 3,000 lb. per sq. inch (214 atm.) this 

 did not happen. 



Compression of the contents of the body cannot account for wrinkling. Water is 

 only compressed by about 4 per cent, at a pressure 15,000 lb. per sq. inch, and it is 

 not likely that the presence of proteins or other cell constituents would make any 

 very great difference; nor is there any gas phase in the body. Moreover, the wrinkling 

 took place rather slowly at the lower pressures, and was never reversed immediately 

 on release of the pressure. From photographs taken before and during the application 

 of pressure, it is clear that wrinkling involves an increase in the length of the peri- 

 meter of the organism as seen in a sagittal profile, and this implies an increase in 

 the surface area of the body. This conclusion has received support from the results 

 of recent experiments in which a relatively low pressure (2,750 lb. per sq. inch) was 

 applied to Discophrya piriformis in the process of feeding. This pressure was sufficient 

 to cause wrinkling but not to prevent feeding. By the time enough food had been 

 taken in almost to fill up the wrinkles, the body was considerably larger than it had 

 been before the application of pressure. 



In those experiments in which the pressure applied was relatively low, the proto- 

 plasm often remained in contact with the expanded cuticle (Kitching, 1954, Plate I), 

 so that it is necessary to conclude that the protoplasmic surface expanded also. The 

 rounding up of the protoplasm which occurred at the higher pressures may be 

 compared with the rounding up of an Amoeba or of a dividing Arbacia egg at similar 

 pressures (Marsland and Brown, 1936; Marsland, 1938). 



On release of pressure, the protoplasm, if separated from the cuticle, often spread 

 back into contact with the latter within the following few minutes or less. This 

 movement must involve either an increase in volume of the protoplasm or an 

 increase in the wrinkling of the pellicle. It cannot be ascribed to an increase in 



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