They are very likely to open their shells wider after they have 

 teen placed in the chromic acid. When chromic acid is not used, 

 it is well to place a bit of wood between the valves to keep them 

 apart when first put into alcohol. Cocaine may be used instead 

 of alcoholized sea water for narcotizing the animals. The animals 

 are preserved in a more distended condition, but its use is not 

 as necessary for lamellibranchs as for gastropods, and the method 

 will be described when the latter are discussed. 



Lima, which has a large number of tentacular filaments 

 around the edge of the mantle, which break off if alcoholized sea 

 water be used, is killed with chromic acid of one-fourth of 1 per 

 cent. Large specimens, however, yield better results if treated 

 with the copper sulphate solution first. 



Scaphopoda. — Dentalium is narcotized with chloral hydrate 

 of 0.2 of 1 per cent, in which it remains from ten to twelve hours 

 or more, and is then put into 70 per cent alcohol. 



Gastropoda. — The use of cocaine for narcotizing all species 

 of gastropods is strongly recommended. The solution consists of 

 2 grams of cocaine powder dissolved in 100 c.c. of 50 per cent 

 alcohol. Place the animals in the least practicable amount of 

 water. Drop in a few drops of the cocaine solution, and after 

 two hours add a few more, and continue the operation until the 

 animals are thoroughly insensible. The action is much slower in 

 winter than in summer. To avoid the contraction into the shell, 

 which is apt to take place with prosobranchs having a spiral 

 shell, even when the narcotizing has seemed to be complete, draw 

 the operculum as far out as possible with a pair of pincers and 

 bind it to the shell. 



As cocaine is not always available, the old methods for 

 treating gastropods will be detailed. It is to be understood that 

 when cocaine is used for narcotizing the subsequent treatment is 

 that 'ndicated below: 



The Placophora and the families of the Patellidae, the 

 Fissurellidae, and the Haliotidae may be prepared in a distended 

 condition by narcotizing them with alcoholized sea water. 



Natica josephinia may be fixed in complete distention by 

 dropping 70 per cent alcohol little by little into the sea water 

 until the animals no longer respond to any stimulus, an operation 

 which often lasts two or three days. Then they are killed by 

 rapidly pouring concentrated acetic acid over them, and they are 

 transferred at once to weak alcohol. If one desires to get perfect 

 specimens he must treat several at once, because out of every lot 

 some are sure to remain more or less contracted. 



Natica millepunctata and N. hebrea, when treated in the 

 manner just described, remain entirely contracted. Good results 

 may be obtained, however, by letting them remain for some days 



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