Chapter 23 



Special Procedures II 



Preparation of Invertebrates for Whole Mounts 

 and Sections 



It is impossible to cover specifically all the members of this huge 

 group of organisms, but certain generalizations can be made which 

 will be applicable to the common forms and perhaps be adaptable to 

 the less common ones. Fixatives can be applied directly to many of 

 them, biu not to others because of their propensity to contract or ball 

 up, pulling in their tentacles or other appendages, and thereby making 

 whole mounts or sections practically worthless. In the latter cases, care- 

 ful anesthetizing or narcotizing must precede killing and fixation. As 

 soon as the narcotization is complete, and before death if possible, 

 fixation can be successful. 



Anesthetizing and Narcotizing Agents 



Magnesium chloride or magnesium sulfate is widely and successfully used 

 on sea anemones, corals, annelids, tunicates and nudibranchs to name a 

 few. Crystalline magnesium sulfate can be tied in a bag suspended above 

 and just touching the water surface, or a 33% aqueous solution siphoned 

 slowly in, controlled by a screw clamp. When the organisms are anes- 

 thetized (no reaction to the touch of a needle), siphon off the water until 

 the animals are barely covered and carefully add fixative. Disturb the 

 animals as little as possible. When partially hardened, transfer to fresh 

 fixative. 



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