AND THE HEBRTDEAN DIAZONA VIOLACEA. 



171 



•regenerative changes in its li£e-liistory, involving, no doubt, profound 

 ^alterations of the metabolism ; and it occurs to me as possible that, if green 

 is the normal colour when in full vitality, those Mediterranean specimens 

 which are described as violet when alive may be in the state preparatory to 

 regeneration when the abnormal life-processes may have caused a chemical 

 change in the pigment similar to that produced in the green Hebridean 

 forms when treated with alcohol. 



EXPLANATION OF THE PLATES, 



Plate 13. 



Fig. 1. Colony of Diazona vwlacea, dredged in the Outer Hebrides, Aug. 1912 ; about 

 one-half natural size. From a water-colour sketch of the living animal. 

 2. From Forbes and Good?ir's coloured figure of " Syntethys hebridkus;' publislied 

 in 1851 ; slight]}'- reduced. 



A. To show the mauve colour of some preserved specimens. 



B. To show the violet colour of the large -Euna ' specimen [fig. 1) after preservation 



in alcohol. 



Plate 14. 



-Fig. 1. Branchial aperture in the test of a Hebridean (green) Diazuna, to show the 6 lobes ; 

 slightly enlarged. 



2. Branchial aperture in the mantle of the same Hebridean Diazona, to show the 



6 lobes ; slightly enlarged. 



3. Part of the test of a violet Diazona, to show the conspicuous pigment cells and 



the colourless test cells ; high power. 

 Figs. 4 to 8. From a Naples specimen, to show the variations in tlie character of the 

 branchial sac. Fig. 8 shows the epithelium on a bar opposite the junction with 

 a connecting duct. 

 9 & 10. From a Mull specimen (Duke of Argyll, 1885), showing variations in numbers 



and sizes of stigmata. 

 11 to 13. From a Plymouth specimen, showing variations in the conditions of 



the bars. 

 14 to 16. From a Hebridean (' Euna/ 1912) specimen, showing variations in the 

 characters of the branchial sac. 

 With the exception of fig. 8, which is a high-power view, figs. 4 to 16 are all 

 of the same magnification, about 40 diameters. 



Addendum. 



'On the Amphipoda, &c., collected from the 'Runa,' by Alfred 0. Walker, 



F.L.S. ; and List of the Echinodermata collected from the ' Runa,' 



by H. C. Chadwick, A.L.S. 



At the meeting of the Society, on December 5th, when the preceding 



,paper was read, Mr. A. 0. Walker made some remarks in regard to the 



>Crustacea collected, and read a list of the Amphipoda and Isopoda which he 



