131 



THIKD KEPOKT upon the NUDIBEANCHIATA 



of the L.M.B.C. DISTKICT. 



By W. a. Herdman, D.Sc, F.L.S., 



I'llOFKSSOK OF NATURAL HISTORY ; AND 



J. A. Clubb, 



ASSISTANT IN THE NATURAL HISTORY DEPARTMENT, UNIVEItSITY COLLEGE, 



LIVERPOOL. 



With Plates YL, VIL, VIIL, IX. 



[Read May 9tli, 1890.] 



Since the last Report, published a year ago *, a large 

 number of Nudibranchs have been collected at Puffin 

 Island, Hilbre Island, and in other parts of the district ; 

 and although no species previously unrecorded have been 

 found, new localities have been added for some of the 

 rarer species, and a number of additional observations 

 upon habits and variations have been made. We have 

 continued some of the anatomical and histological investi- 

 gations on the structure of the cerata commenced last 

 year, and have instituted a comparison between the con- 

 ditions of the various dorso-lateral ridges and processes 

 in the different genera. We also record here some 

 experiments made in the fish tanks of the Liverpool 

 Aquarium with the object of testing the theory proposed 

 by one of us that the chief function of the cerata or dorsal 

 papillae is, according to their condition, to contribute to 

 the inconspicuous and protective appearance of the animal 

 or, in other cases, to render it conspicuous and warn 

 predaceous animals of some special offensive property. 



* Proc, Biol. Soc, L'pool, vol. iii., p. 225. 



