42 



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

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

 pigmented epithelium ; this is discussed below. 



The tentacle (fig. 2-3) is covered by a layer of coluninai' 

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

 elongated nuclei, and they do not ap])ear to be closely 

 packed when the tentacle is moderately extended. They 

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

 are ordinary epithelial cells, sensory cells and goblet cells. 

 The sub-epithelial layer is a very compact felt- work of 

 hbres, many of which are undoubtedly iieiwous. Beneath 

 this is a mass of muscle hbres of tlie usual type, arranged 

 ill bundles surrounded by connective tissue. Most of 

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

 retractors ; there are also a few oblicpie hbres, but no 

 circular muscle occurs. The ieutacle nerve goes down 

 the centre, receiving its hbres from llic sul)-cpiiliclial 

 region, and hnally 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, the 

 lateral surface near the ti]) just barely grazing 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 thai 

 function, his conclusion seems more than is Avarrautcd b\' 

 evidence. Limpets with the tentacles cut short have 

 " homed " successfully in several cases, and two animals 

 Avere observed at Granton doing- the same, thoush the 

 entire tentacles had been removed. The pigment on the 



