248 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



them well with water. In the center of the dish is placed a heavy but short 

 vial containing only a few drops of chloroform. The whole is covered with a 

 bell-jar. The chloroform may also be dropped on a piece of cotton or blot- 

 ting paper and placed on a large piece of cork floating on the surface of the 

 water, or simply left on the table. It must, however, never come in direct 

 contact with the water. In from fifteen minutes to two hours, or when the 

 worms are fully stretched out, they are ready to be killed with the fixative. 



A method to be recommended in handling delicate and thin-skinned worms 

 is to place them in water to which from time to time are added a few drops of 

 a saturated solution of bichloride of mercury in water. In half an hour the 

 worms should be fully stretched out and ready to be fixed. 



Fixatives and Imbedding. 



The best and most practical fixative for Oligochaeta the author finds to be a 

 solution of bichromate of potassium with acetic acid, according to the follow- 

 ing formula: — 



Bichromate of potassium 3 parts. 

 Glacial acetic acid 6 parts. 

 Water 100 parts. 



The worms are fixed in this solution for about twenty-four hours and after- 

 wards washed in running water for several hours until no trace is left of the 

 yellow color. 



This fixative is cheap and easily carried on collecting trips; it has an advan- 

 tage over sublimate in being non-poisonous and requiring no iodification; it 

 allows of excellent staining and fixes better than sublimate-acetic. 



A cheap fixative and preservative for the use of traveling collectors consists 

 of two per cent, of formaldehyde in 33 per cent, of alcohol. This preservative 

 allows of good staining and does not make the specimens brittle. It is, how- 

 ever, inferior to the sublimate-acetic and the bichromate-acetic fixatives. 

 The worms are dropped into the solution, which should be replaced by fresh 

 after twenty-four hours. 



Worms which are to be sectioned lengthwise should not be as straight as 

 those which are to be sectioned transversely. If they are slightly curved it 

 is much easier to orientate their ventral and dorsal sides when placing them 

 in the paraffin imbedding. The worms curve either ventrally or dorsally, and 

 even the slightest curve will enable one to place them so that the sections 

 will pass directly through the dorsal and ventral line. Sections destined for 

 transvere sectioning should be perfectly straight. This is best accomplished 

 by placing them between thin glass rods. 



As soon as the worms are dead and before they become stiffened place 

 them in a dry, shallow dish with a flat bottom. After straightening each 

 worm out place along side of it a round glass rod, as thick or slightly thicker 

 than the worm. By alternating worms and glass rods, the whole bottom of 

 the dish may be covered and the worms kept perfectly straight. 



The fixative is at first applied slowly, drop by drop, so as not to disturb 

 the specimens; but as soon as they are sufficiently hardened they should be 

 entirely covered with the fixative. If the worms are large it may be neces- 

 sary to replace the liquid by fresh. More than four hours immersion is not 

 advisable. 



