131 
THIRD REPORT upon the NUDIBRANCHIATA 
of the L.M.B.C. DISTRICT. 
By W. A. Herpman, PD.Sc., F.L.S., 
PROFESSOR OF NATURAL HISTORY; AND 
Je Ae OnuBe: 
ASSISTANT IN THE NATURAL HISTORY DEPARTMENT, UNIVERSITY COLLEGE, 
LIVERPOOL. 
NVirchasizlatess Wal Vill VEL. IEXe 
[Read May 9th, 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 
papille 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. ii., p. 225, 
