FIXATION OF MOLLUSOA. 355 



" F lemming/' and got a very poor preparation. The very 

 similar 8. pinnata is fixed perfectly in this medium. 



Mollusca. 



706. Fixation of Mollusca. Two groups at least amongst the 

 Mollusca offer considerable difficulties in the way of fixation 

 Lamellibranchiata and Gastropoda. 



If it be attempted to take living and normal Lamelli- 

 branchiata from the water they are contained in, in order to 

 throw them into a fixing solution, they invariably withdraw 

 their siphon and foot, shut their valves, and die in a state of 

 contraction. And if it be attempted to open the shell by 

 force after death, the mantle is generally injured and it is 

 impossible to get the foot and siphon into the extended state. 

 DE CASTELLARNAU (La Estacion Zoolog. de Napoles, Madrid, 

 1885) advises that they be killed by the method of EISIG and 

 ANDRES described for Actinias in 13. Before dying, the 

 animals protrude largely their feet, siphons, branchiae, and 

 tentacles, and die with their shells open. They may be fixed 

 as soon as insensibility has supervened, by bringing them into 

 picro-sulphuric acid, or some other rapidly killing fixing agent. 



In order to demonstrate the absence of the supposed aqui- 

 ferous pores in the root of Lamellibranchiata, FLEISCHMANN 

 (Zeit. /. wiss. ZooL, xlii, 1885, p. 376) proceeds as follows : A 

 mussel is quickly seized at a moment when the foot is fully ex- 

 tended, and the two valves of the shell are forcibly pressed 

 together, so as to prevent any flowing back towards the 

 interior, of the liquid contained in the foot. The foot may 

 then be fixed by holding it for a few minutes in hot sublimate 

 solution. 



Tlic same methods recommended for Lamellibranchiata 

 sometimes give good results with Gastropoda. The asphyxia- 

 timi method has been described in 18. 



The quantity of mucus that exists in the integument of 

 Gastropoda is often a serious obstacle in the way of preparation. 

 MARCHI (Arr/i.f. mik. Anat., 1867, p. 204) finds that if a 

 living Limax be thrown into moderately concentrated salt- 

 solution it will throw off enormous quantities of mucus, and 

 die in a few hours. The epidermis will be found well pre- 

 served. If the animal be thrown into osmic acid or Miiller's 



