MOLLUSCS, TUNICATES 381 



then kill rapidly with formalin. In the case of cal- 

 careous material, transfer at once from the formalin 

 to 70 per cent, alcohol. Other reagents may be used 

 instead of formalin, but are best employed hot. 



Nudibranchiata. — Kill by plunging suddenly into 

 glacial acetic acid. Transfer at once to weak and 

 then to 70 per cent, alcohol, or transfer at once to 

 5 per cent, formalin. The larger forms, such as 

 Archidoris tuberculata, are best" killed with menthol 

 or anaesthetized by the alcohol method, and preserved 

 in formalin-spirit. 



Gastropoda and Lamellibranchiata. — These may often 

 be killed expanded by putting crystals of menthol on 

 the surface of the sea water containing them. Alcohol, 

 added very slowly to the sea water, will sometimes 

 produce the same result, but is very uncertain. After 

 killing, any of the ordinary preserving fluids may be 

 used, formalin-spirit being good for general purposes. 

 In the case of lamellibranchs, it is a good plan to slip 

 a wedge of wood or cork between the open valves, to 

 prevent them closing again. 



Simple and Compound Ascidians. — Anaesthetize with 

 menthol, and preserve in 2 per cent, chromic acid 

 solution, or in any of the ordinary preserving fluids. 



The free-swimming Tunicates (Salpa, Doliolum, 

 Pyrosoma, etc.) are easily preserved by simply placing 

 them in formalin 10 per cent. Allow them to soak for 

 a day or two, and then increase the strength of the 

 formalin. The addition of a very small quantity of 

 chromic acid 1 per cent, solution to the formalin is an 

 advantage, as it helps to harden the gelatinous test. 



Salpae arranged in chains frequently become isolated 

 when only formalin is used. A mixture of corrosive 

 sublimate and acetic (10 c.c. glacial acetic and 90 c.c. 

 corrosive sublimate) is very good for their retention 



