126 PART I. GENERAL ACCOUNT 



which can surely be called an "evasive reaction". These conclusions are 

 confirmed by the histological findings also: they possess giant nerve fibres 

 apparently serving for the rapid propagation of impulses to the longitudinal 

 musculature which shortens part of the trunk (Ivanov, 1958b). 



There is apparently no necessity for the animal to poke out the whole 

 tentacular apparatus for collecting food particles in the intertentacular cavity 

 (through which runs the stream of filtered water). It may be sufficient if only 

 the distal end of the crown is pushed out. How Siboglinum collects its food 

 is not clear. Amongst several possibilities one may suggest that Siboglinum 

 gathers food particles from the surface of the mud, searching the surrounding 

 area of the sediment with the single tentacle. And then the tentacle perhaps 

 twists up into a corkscrew around a small quantity of food particles and then 

 withdraws into the tube where digestion takes place. [This has been seen to 

 happen — D.B.C.]. It may be that all Pogonophora periodically withdraw 

 into the tube for digestion of the food gathered by the tentacular apparatus. 

 It cannot be doubted, however, that the female, having laid the eggs in the 

 anterior part of her own tube, is forced to stay in the bottom of the tube all 

 the time that the embryos are developing. 



These ideas are purely speculative for the moment and need examination 

 on the living animal. 



[Kirkegaard (1961) has attempted to observe Siboglinum ekmani in the 

 living state. They live well in the laboratory if kept cool, but he never saw 

 them emerge from the tube and suggested that they were light-shy. This has 

 been confirmed and it is necessary to use dim red light to observe the be- 

 haviour of the animal, which will only poke its front end out of the tube in 

 the absence of the rest of the spectrum. No specific light-receptors have been 

 demonstrated and the whole animal may well be equally sensitive to light — 

 D.B.C.] 



