On suction in Suctoria 



volume of the protoplasm due to decompression, as it takes place too slowly. Al- 

 though in some cases there was an indication of a swelling, some time after release 

 of pressure, associated with a prolonged stoppage of the contractile vacuole, it is by 

 no means clear that this accounted for the rather rapid spread of the protoplasmic 

 surface which was sometimes seen. 



The cuticle remained wrinkled for many hours after the release of pressure. How- 

 ever the wrinkles slowly disappeared and eventually cuticle and protoplasm became 

 rounded in outline. Wrinkles formed at 2,000 lb. per sq. inch were observed to dis- 

 appear even while the pressure was maintained, and in other cases in which limited 

 wrinkling was induced by rather brief exposure to high pressure the wrinkles dis- 

 appeared within a few minutes after release of the pressure. It may therefore be sug- 

 gested that there is a mechanism by which the fit of the pellicle to the protoplasm is 

 constantly subject to adjustment. This mechanism resides in the protoplasmic surface 

 and is likely to be enzymatic. It was noticeable that after release of pressure, if there 

 was some portion of the pellicle which was not brought into contact with the proto- 

 plasmic surface by the spread of the latter, this portion did not become remodelled, 

 but persisted as an excrescence. Mechanisms for the adjustment of pellicular fit must 

 be widespread in the Protozoa. The tendency of the protoplasmic surface to expand 

 when the cuticle allows it to do so is evidently opposed by high pressure, and only 

 reaches its full development after the pressure has been released. 



FEEDING IN SUCTORIA 



Let us now return to the process of feeding in Suctoria. There is clearly a process 

 of activation. In Choanophrya infudibulifera suction is not provoked by carmine par- 

 ticles, but is initiated by genuine food (Collin, 191 2). In Discophrya piriformis the 

 expansion of the body surface follows attachment of the tentacles to the prey. The 

 expansion of the cuticle is somewhat reminiscent of the formation of a fertilization 

 membrane, although it is carried out without the elevation characteristic of the 

 latter. The cuticle of Discophrya is probably also made of protein. It is not clear 

 whether expansion of the cuticle merely permits expansion of the protoplasmic 

 surface within it, or whether activation directly stimulates the protoplasmic surface 

 to expand. It is perhaps relevant that, on the application of pressures of 10,000 lb. 

 per sq. inch (680 atm.) or more, there was usually an apparently simultaneous 

 expansion of the cuticle and separation from it of the protoplasmic surface, and that 

 on release of pressure the protoplasmic surface spread, and made contact with the 

 expanded cuticle. This shows that expansion of the cuticle can at least occur indepen- 

 dently, although it may well be brought about by reactions at the protoplasmic 

 surface. So far I have not been able to induce wrinkling in Acineta by the application 

 of high pressure. This suctorian has a very loosely fitting cuticle or case, with plenty 

 of room inside for expansion during feeding, so that presumably a mechanism 

 for the rapid expansion of the cuticle is unnecessary. 



It is not known whether expansion of the body surface of Discophrya piriformis 

 merely makes room for food material driven in by other means, such as peristalsis 

 of the inner tubes of the tentacles, or whether this expansion actually creates a 

 suction. A more detailed study of the peristaltic movements of the tentacles is 



201 



