788 THE AMERICAN NATURALIST. (VoL. XXXIX. 
3. Preserving.— Place the worms in 50% alcohol and leave 
for a day or two; the alcohol will become discolored by chromic 
acid. Change to 70% and leave a day or two longer. Then 
change to the same grade (70%) for final preservation. 
The alcohol will complete the process of removing free acid 
and will further harden the tissues. Stronger grades of alcohol 
than 70 % are not advisable for preservation, as they may cause 
the more delicate tissues to become brittle. 
(b Alcohol Method. 
Kill as directed under chromic acid method. Place the 
worms in 50% alcohol, keeping bodies as straight as possible. 
Leave 4 or 5 hours, then place in 70% alcohol and leave over 
night. Next morning place in 96% alcohol to harden them, 
and leave all day. Change to 70% alcohol for final preserva- 
tion. i 
Choice of Methods.— Specimens hardened in chromic acid are 
most satisfactory for general dissection purposes. The tissues 
are firm and leathery, and are not affected by water during dis- 
section, hence they may be dissected under water instead of 
alcohol. This is a decided advantage. The largest and best 
marked specimens should be put up in this way. 
The alcohol method of fixing is not so satisfactory for most 
purposes ; the body wall and tissues generally are too soft to be 
conveniently handled unless the dissection is done under alcohol. 
But the method has the advantage of simplicity, and the smaller 
and more poorly marked specimens may be put up in this way 
for use in case other material runs short. Alcoholic specimens 
do very well for the study of the nervous system. 
Fresh Specimens are not only necessary for the study of the 
living worm, and for demonstrations of cilia, blood, coelomic 
fluid, spermatozoa, etc., but are best for the study of the circu- 
latory system and the nephridia. 
For studying the circulatory system the living specimen may 
be stretched out in a dissecting tray and fastened with a pin 
through each end of the body ; if desired it may first be stupe- 
fed with alcohol. The dissection should be carried on under 
