658 PROCEEDINGS OF THE ACADEMY OF [Dec.^ 



and generous assistance. To Dr. ISIontgomery, who has more di- 

 rectly supervised my work and kindly helped me in many ways, I 

 am especially grateful. I would also thank Dr. C. O. Whitman for 

 the courtesies extended me at the Marine Biological Laboratory at 

 Wood's Hole, and I am indebted to Dr. Wesley R. Coe for many 

 kindnesses. 



Methods. — Owing to the great contractility of the Neraerteans, 

 it is best to use some stupefying agent before fixation, otherwise 

 the specimen becomes so twisted that it is unfavorable for section- 

 ing. After removing the shme sheaths with a needle, the worms 

 were usually placed in a shallow dish of sea-water, and crystals of 

 magnesium sulphate were slowly added. If dropped in too quickly 

 they will irritate the worms and fragmentation will occur. In this 

 solution the worms were left until they ceased to respond when 

 touched, the time varying from one and a half to three hours, 

 according to the amount of the sulphate. When the worms were 

 sufficiently relaxed the water was drawn off, and the killing fluid 

 added; or they Avere lifted out of the water with brushes and 

 placed in the fixative. 



The fixatives used are (1) corrosive sublimate, a concentrated 

 solution in fifty per cent, alcohol, for thirty minutes; an excellent 

 general fixative, and one that has been extensively used in this 

 Avork. (2) Gilson's mercuro-nitric mixture, formula ac<;ording 

 to Lee (1896), for about half an hour; to be highly recom- 

 mended, especially for the structure of gland cells and connective 

 tissue. (3) Flemming's fluid (chromo-aceto-osmic acid), for 

 twenty-four to sixty hours; especially good for nerve tissue and 

 cilia. (4) Flemming's fluid (stronger mixture), for forty-eight 

 hours, followed by pyroligneous acid for twenty-four hours. After 

 employing this method the material may be sectioned and mounted 

 without staining. It is excellent for tracing nerves, and for the 

 gross anatomy of most parts, but it is not adapted for histological 

 or cytological details, except for cilia. Specimens fixed in this way 

 may afterward ^be stained with iron-hiematoxylin, but the results 

 are not so good as when Flemming's fluid alone is used. (5) 

 Ninety -five per cent, alcohol ; a good fixative, except for the body 

 epithelium. 



The stains used are Ehrlich's h?ematoxyhn, undiluted, fifteen 

 minutes to one hour, washed with alcohol containing a few drops 



