762 ON THE CH^TOSOMATID^, 



been fixed before washing, but six hours' search through a second 

 lot of material (fresh) from the same spot yielded only a single 

 specimen. A careful examination of shells and seaweed revealed 

 the living worms still clinging to them, after a very thorough 

 washing. It is most difficult to detect the worm against the 

 dark background of seaweed, so that, unless living specimens are 

 required, the material collected is fixed before washing. With 

 C. haswelli, there is not the same difficulty, as they wash off 

 much more readily. 



Methods of Preparation. 



Various fixatives have been tried — formalin, sublimate-acetic, 

 Carl's, glycerine-alcohol, and 70% alcohol, hot and cold. Formalin 

 or sublimate-acetic, which for bulk-fixing are the most con- 

 venient, seem to give as good results as any. 



Stains used in the preparation of whole mounts include Erlich- 

 hsematoxylin, picro-haematoxylin, picro carmine, borax-carmine, 

 and para-carmine. The picro-stains give very poor results. 

 Erlich-hsematoxylin and borax-carmine seem to be the most satis- 

 factory; but the worm requires prolonged immersion in these, 

 especially in the first, owing to the thickness of the cuticular 

 covering. The length of time required varies with the species; 

 three or four days for the species which have a very thick cuticle. 



Clearing is a very difficult process, as most clearing agents, 

 unless very carefully applied, shrivel and distort the animal. 

 The more delicate C. haswelli mounts well in glycerine-jelly, 

 when cleared for some time in glycerine-alcohol (glycerine, 10%; 

 alcohol, 90%) under a bell-jar; but for the species with thicker 

 cuticle, clove-oil or cedarwood-oil must be used, and the mounting 

 done in Canada balsam. I have found clove oil the best, but it 

 is necessary to add it very gradually, drop by drop, to the abso- 

 lute alcohol, bringing up to pure clove-oil only after a day or two. 



For section-cutting, the double embedding, paraffin-celloidin 

 method was used. A few worms were embedded direct in paraffin, 

 after clearing in cedar-oil, but the result was unsatisfactory; as 

 was also the case when a celloidin-block was dispensed with, the 

 worm being transferred direct from ^% celloidin-solution to 



