No. I.] THE METAMERISM OF NEPHELIS. 1 9 



ware cooking dishes, known to tlie trade as nappies. In some 

 instances I supplied the aquaria with a layer of mud and bottom 

 debris, together with a few plants such as Ceratophyllum or 

 Valisneria. When such an aquarium is covered with a glass 

 plate it will keep fresh and clean for a long time and will 

 furnish considerable food for the leeches. Generally, however, 

 I used the plain dish, cleaning out the debris and slime and 

 changing the water when necessary. I fed chopped fresh- 

 water clams, but I do not doubt that salt-water clams will serve 

 as well. I have kept individuals for over a year in normal 

 condition and have raised many young under these conditions. 

 When they are first transferred to the aquarium it must be 

 covered for a day or two, to prevent escape. For superficial 

 examination the leeches were killed in very dilute chromic 

 acid, ye to y^ per cent solutions. There is one period just 

 before the acid penetrates very deeply when the surface mark- 

 ings stand out very clearly. The leeches usually extend them- 

 selves very well, and if killed in a wax tray they may be guided 

 by pins. The best medium for histological details is a ^ to 

 yi per cent solution of chromic acid, allowed to act for at least 

 24 hours. The stains used were borax carmine, Delafield's 

 haematoxylin, and Bizzozero's picro-carmine. The macroscopic 

 characters of the nerve chain were studied from maceration 

 preparations. The leech is killed in a 20 per cent solution of 

 nitric acid and left in it for from 24 to 36 hours, or until the 

 skin and muscles can be easily removed with a porcupine 

 bristle or a glass rod drawn out to a point. These were all 

 carefully dissected away, leaving the chain entire. After 

 thorough washing, the chain may be slightly stained in borax 

 carmine and mounted in glycerine. 



A number of details were worked out by the use of Haller's 

 fluid. For example, the head was cut off, slit open on the 

 ventral or dorsal side as wished, and killed in Haller's fluid 

 while it was flattened under a piece of glass. After two days 

 the specimen was transferred to glycerine. 



The method that has given me the best results for nerves 

 and sense organs is a gold chloride process kindly given me 

 by Miss Julia B. Piatt. It is so simple, so sure, and so exqui- 



