MAKING WHOLEMOUNTS 43 



author prefers his own mixture (p. 14) for the purpose, and fixed in a hot 

 mercuric-acetic mixture. 



Platyhelminthes. Some of the smaller fresh-water Turbellaria (e.g:, Vortex, 

 Microstomum) may be narcotized satisfactorily by adding small quantities of 

 2 per cent chloral hydrate to the water in which they are swimming. Another 

 good technique is to isolate the forms in a watch glass of water and place the 

 watch glass under a bell jar together with a small beaker of ether. The ether 

 vapor dissolves in the water and narcotizes these forms excellently. A detailed 

 account of the method of handling the liver fluke is given on page 95 and 

 may be employed satisfactorily for other parasitic flatworms. 



Annelida. Small marine free-living Polychaeta make excellent wholemounts 

 and do not usually require narcotization before killing. However, they should 

 be stranded on a slide, and a very small quantity of the fixative should be 

 dropped on them, so that they die in the flat condition which makes subsequent 

 mounting possible. Much more realistic mounts are obtained by this means 

 than if the animals are laboriously straightened before fixing, because they 

 usually contract into the sinuous wave which they show when swimming. There 

 seems to be no certain method of fixing the Nereids with their jaws protrud- 

 ing. One has to rely on chance to obtain one in this condition. 



Fresh-water Oligochaetes. These are best narcotized with chloroform, 

 either by adding small quantities of a saturated solution of chloroform in 

 water or by placing them in a small quantity of water under a bell jar in 

 which an atmosphere of chloroform vapor is maintained. Leeches are rather 

 difficult to handle, and the author has had greatest success by placing them in 

 a fairly large quantity of water to which is added, from time to time, small 

 quantities of a solution of magnesium sulfate. As soon as the leeches have fall- 

 en to the bottom, much larger quantities of magnesium sulfate can be added, 

 which will leave the leeches, in a short time, in a perfectly relaxed but not 

 expanded condition. Then they should be flattened between two slides and 

 fixed in Zenker's fluid. After the specimens have been fixed sufficiently long 

 to hold their shape when the glass plates are removed, they are transferred for 

 a couple of days to fresh fixative and then washed in running water overnight. 



Bryozoa. Marine Bryozoa may be narcotized without the least diflficulty by 

 sprinkling menthol on the surface of the water containing them. Subsequent 

 fixation is best in some chrome-acetic mixture. It is usually recommended that 

 fresh-water Bryozoa be narcotized in a cocaine solution, but the author has 

 found menthol just as good and very much easier to use. Fresh-water Bryozoa 

 should be fixed directly in 4 per cent formaldehyde since they shrink badly 

 in any other fixative. 



