42 



corrugated; the apical part is pigmeuted. At the base of 

 the outer side is a small pit (the eye) lined by deeply 

 pigmeuted epithelium ; this is discussed below. 



The tentacle (fig. 2-3) is covered by a lay(>r of cohunnar 

 epithelium, the cells of which are long and narrow, willi 

 elongated nuclei, and they do not a})pear to be closely 

 packed when the tentacle is moderately extended. They 

 have a cuticle, which stains yellow with picric acid. There 

 are ordinary e])ithelial cells, sensory cells and goblet cells. 

 The sub-epithelial layer is a very conii)act felt-work of 

 fibres, many of which are undoubtedly uervous. lieueath 

 this is a mass of muscle fibres of the usual type, arranged 

 in bundles surrounded by connective tissue. Most (tf 

 them go from base to tip, and so are longitudinal tentacle- 

 retractors ; there are also a few oblique fibres, but no 

 circular muscle occurs. The tentacle nerve goes down 

 the centre, receiving its fibres from the sub-epithelial 

 region, and finally entering the cerebral ganglion, 

 which is at the base of the tentacle. There is a 

 good deal of loose tissue in the tentacle, as might 

 be expected in an organ with such a high degree of 

 contractility. 



The animal waves its tentacles as it moves along, llic 

 lateral surface near the tij) just barely gra/cing the rock 

 surface over which it is creeping. This lateral surface 

 near the tip is the region of maximum sensitiveness. The 

 tentacles are undoubtedly tactile, and Professor Lloyd 

 Morgan considers them as the organs of the well-known 

 "homing"" sense, but, though they may assist in that 

 function, his conclusion seems more than is warranted by 

 evidence. Lim])ets witii the tentacles cut short have 

 " homed '" successfully in several cases, and two luiimals 

 Avere observed at Granton doing the same, though the 

 entire tentacles had been removed. The pigment on the 



