112 ON COLLECTING INVERTEBRATE ANIMALS 
MOLLUSCA. 
Lamellibranchs and Heteropods should be narcotized in alcoholized 
sea-water. To avoid the closure of the valves of Lamellibranchs 
on immersion in 70 per cent, alcohol, little plugs of wood should be 
placed between the margins of the valves. The same result may- 
be effected in the case of large Prosobranchs after narcotization by 
tying the operculum to the shell. 
Of the Opisthobranchs the Solids may be best preserved by 
pouring over them concentrated acetic acid in volume equal to 
or double that of the sea-water containing them. Dorids should 
first be narcotized by gradually adding 70 per cent, alcohol to their 
sea-water, and then killed with concentrated acetic acid or boiling 
sublimate. The larger forms may be killed in from 1 to 5 per 
cent, chromic acid. 
Pteropods are preserved well in Perenyi's fluid for fifteen minutes, 
whence they are passed to 50 per cent, alcohol. Gymnosomatous 
forms should be first narcotized with 1 per cent, chloral hydrate, and 
then killed in acetic acid or sublimate. 
Decapod Cephalopods may be fixed directly in 70 per cent, alcohol, 
if an opening be made on the ventral surface to allow the alcohol to 
reach the internal parts. After twenty-four hours the alcohol 
should be poured off and replaced by a fresh quantity. After three 
days' immersion in this second quantity of alcohol, it is recommended 
that Cephalopods be preserved in 5 per cent, formalin. Formalin 
does not destroy the pigments of the integument. 
