KITCHING 



the diameter of the inner tube of the tentacles is 05^, that three tentacles are active, 

 and that the tentacles are 25^ in length, it was calculated (Kitching, 1952a) that 

 for a viscosity twice that of water a pressure difference of about 1 cm. of water would 

 be needed. If the viscosity of the food material is greater, the pressure required would 

 be proportionately higher. 



THEORIES OF SUCTION 



Although the positive hydrostatic pressure within the prey itself might provide the 

 necessary force, it is clear that in the feeding of Suctoria a suction must be exerted. 

 Complete flagellates have been observed inside Tokophrya cyclopum (Collin, 191 2). 

 The ingestion by Tokophrya infusionum of whole ciliates, nucleus, pellicle, and all, 

 has been watched and described by Iziumov (1947). Finally, according to detailed 

 observations by Collin (1912, p. 261), in confirmation of Hartog (1901), the suctorian 

 Choanophrya infundibulifera sucks in particles of crushed Cyclops from a distance, like a 

 miniature vacuum-cleaner. There is no doubt that Suctoria really do suck. 



To explain suction, two plausible theories have been suggested, as well as some 

 others. Peristaltic waves travelling down the inner tube of the tentacles could drive 

 fluid along the tentacles into the body (Collin, 191 2), or the body surface might 

 actually increase in area and so create a suction (Kitching, 1952a). 



Waves have actually been seen by Collin (191 2, p. 265) travelling down the inner 

 tube of the tentacles of Tokophrya cyclopum, Discophrya steinii, and Choanophrya infundi- 

 bulifera. On the other hand waves seen by Dragesco and Guilcher (1950) in Disco- 

 phrya piriformis proceeded in both directions and appeared to them to be inadequate 

 to explain the process of feeding. They also failed to find waves in the tentacles of 

 Dendrocometes paradoxus. 



The possibility of an active increase in the surface area of the body was suggested 

 by some observations made during the course of experiments on the effects of feeding 

 on the activity of the contractile vacuoles of Discophrya piriformis. I noticed that 

 occasionally the body surface of the suctorian became wrinkled soon after the capture 

 of a ciliate, and that later, with the uptake of food into the body, the wrinkles dis- 

 appeared. This wrinkling might be due either to a decrease in volume of the body 

 or to an expansion of the body surface. Photographs showed that, at a stage when 

 just enough food had been taken up almost to cause the wrinkes to disappear, the 

 body was considerably larger than it had been before the wrinkling occurred. It 

 therefore appeared that the wrinkling was due at least in part to an increase in surface 

 area. It is true of course that there might also have been a temporary decrease in 

 body volume, such as might be produced by an injection of material into the prey, 

 but there is no positive evidence in favour of this view, nor will it by itself explain the 

 observations. 



It was found possible to induce wrinkling regularly in Discophrya piriformis which 

 had been grown in dilute sea water (5 or 10 per cent.) by feeding it on Paramecium in 

 a partially dehydrated state. The Paramecium was transferred from a freshwater 

 culture to the same dilute sea water a few minutes before it were offered to the 

 Discophrya, so that it had lost water by oxosmosis. The Discophrya became wrinkled 

 within a few minutes, and remained so for an hour or more, but ultimately filled 

 up with food so that the wrinkles disappeared. When the wrinkles were about to 



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