MORPHOLOGY OF MELIBE 515 



regularly in length.' Gould (1852), describing M. 1 eon in a, 

 says : ' The mouth is inferior and surrounded by a series of 

 long cirrhi, each of which has an independent motion." 



(1) The Cirrhi. 



The cirrhi (PI. 27, figs. 1, C, 10, Ic, Oc, PI. 28, 17, Ire, Ore) 

 have an inner median axis (PI. 28, figs. 11, 12, Cg, 13, Cya) from 

 which radiating fibres pass to the periphery (BJ). The inner axis 

 seems to consist of a series of nerve ganglia from which fibres 

 radiate to the periphery of the cone-like cirrhus, ending in the 

 basal layer of the epidermis (PI. 28, fig. 11, Oe, le). In other 

 words, a cirrhus is a conic structure having an epithelial wall 

 resting upon a delicate connective-tissue framework, with an 

 inner axis which passes from the apex to the base of the cirrhus, 

 and from this axis fibres radiate to the epithelial walls of the 

 cone. These fibres have the resemblance of nerve-fibres, 

 particularly in their relation to the cells in the ganglionic 

 axis and to the epithelium of the epidermis. In one of the 

 angles, formed by the radiating fibres at the axis, is a large 

 bladder-like structure around which the fibres pass, and at the 

 periphery are placed large and small cells (PI. 28, fig. 13, Pc) 

 the inner part being reticular in structure (Ir) and containing 

 apparently no cells, or a few only (PI. 28, figs. 11, 12, 13, Ir). 

 The cirrhi are probably tactile or gustatory in function. Some- 

 thing to that effect was demonstrated experimentally (Agers- 

 borg, 1922a: p. 441). Sedgwick (1898: p. 366) writing on the 

 gasteropods in general and opisthobranchs in particular says : 

 ' Tactile organs are represented by the tentacles, the edges 

 of the lips, which are often folded (labial palps), the tentacular 

 and lobe-Uke prolongations which are found here and there 

 on the head, mouth, and foot.' It should be remembered that 

 there are sometimes two pairs of tentacles in nudibranchs ; 

 the anterior pair being the one referred to here ; the posterior 

 is the so-called rhinophoria of many authors, which, however, 

 do not seem to be olfactory in function (iVgersborg, 1922 a: 

 423-44). 



M m 2 



