INVERTEBRATE ZOOLOGY. 97 



but the following may be taken as a mean estimate. Specimens are not 

 harmed by exceeding the time in the stain or in 70^, btit the higher alcohols 

 and the turpentine render them hard and brittle. 



Preparing an object in toto for viicrotorne sections. 



1. A specimen, preserved as above, is taken from the bottle of 70 ^r and 



placed in borax carmine — twenty-four hours. 



2. Take from the stain and place in " acid 10 '/c " i. e. 70 ^^ + a few drops 



of HCl. Watch the piece and see it turn from a dull maroon to a 

 bright scarlet. The change should be moderately slow (5-10 min- 

 utes). A too rapid change denotes an excess of acid, a too gradual 

 change denotes too little. This should be remedied in either case. 

 The piece should remain until it is thoroughly penetrated hy the 

 acid alcohol (10-20 minutes). 



3. Place in clean 70 ;? (2-6 hours). 



4. 95 % alcohol (6-12 hoiirs). 



5. too 7/ alcohol (4-8 hours). 



6. Turpentine (4-8 hours). 



7. Melted pai-affine (2-4 hours). 



8. Imbed. 



Small Stender dishes are the best to lase for the work of the fluids. The 

 100 '/r should 1)6 kept in a tightlj' corked bottle. Bottles are often conveniently 

 used for carrying al)out when changes are to be made out of lal)oratory hours. 

 A preparation made in this way is amply sufficient for an entire class, and 

 may be made by one i)erson, the students taking turn in thus preparing the 

 class specimens. Sections through the "liver" (better ItejMito-jxtncreas) or 

 through the intestine are very instructive and simple in structure. 



Type XII.— Porcelllo sp ? 



69. Collecting and preserving. This is the common '■ sow-bug" or " damp 

 bug," a terrestrial Crustacean foimd in damp shady woods beneath stones, and 

 is often met with under bricks and boards in barns and cellars. Simple im- 

 mersion in 70 ',, is sufficient to kill and preserve them for the study of the ex- 

 ternal parts, and each student before the approach of cold weathei- should 



