21 



are very bristly. Water alone may be used for the washing if 

 salt solution cannot be had, but specimens, especially Nematodes, 

 must not be left long in it. 



Killing. After washing, the specimens must be killed with 

 some reagent which leaves them in a suitable condition for 

 subsequent examination — i.e. which " fixes " their tissues in a 

 condition as nearly as possible approaching that of life. 



The- most generally useful reagent is Corrosive Sublimate 

 (see list of reagents). The effect is more instantaneous if the 

 solution be heated, and the animals then plunged into it ; but it 

 may also very well be used cold. An hour or two in this solution 

 will be long enough for the largest specimens ; for smaller ones a 

 few minutes will suffice. For necessary treatment after corrosive 

 sublimate, see this heading in the list of reagents. 



Formalin (10 per cent, solution) is also good for most 

 parasites, except for Nematodes, but it cannot be recommended 

 for the majority of marine worms ; specimens left in this reagent 

 for 24 hours can then be transferred to the weaker solution, or to 

 alcohol. 



For killing parasitic worms, see also other methods given l^elow. 



Narcotizing. As it is desirable to get the animals to die in an 

 expanded condition, it is useful in some cases to anaesthetize them 

 before killing. This is especially the case with Nemertines, and 

 worms which live in tubes. They may be placed for from 

 6 to 12 hours in a solution of chloral hydrate in sea water 

 (1 per cent.), or a few of the crystals may be simply added to the 

 sea water in which they lie. When fully extended and showing 

 no sign of sensation, they may be preserved with formalin or 

 alcohol. Cocaine may be used with advantage instead of chloral 

 hydrate. 



Another method is to place the worms in a shallow dish of sea 

 water, and gently pour about Jq P^-i't of strong alcohol on the 

 surface. This will slowly mix with the water and anaesthetize 

 the animals gradually. They can then be transferred to alcohol 

 to harden, and preserved in it. 



Some of the free-living Polychaeta must be treated in this way, 

 or they will In-eak themselves into a number of little pieces when a 

 killing reagent is added. 



Note. — In tropical countries narcotizing is sometimes found 

 difficult, owing to the fact that decomposition sets in before the 

 anaesthetic has had time to take effect. In such cases the alcohol 

 method will be found to give better results than chloral hydrate. 



