1911] Watson: The Genus Gyrocotyle. 383 



D. GENERAL MORPHOLOGY AND HISTOLOGY OF 

 GYROCOTYLE. 



I. MATERIAL AND METHODS. 



The structure of the worm has been studied in living speci- 

 mens, in whole mounts stained and cleared, and in serial sections. 

 The following killing fluids were used: Gilson's fluid, aceto- 

 sublimate, Zenker's fluid and Vom Rath's mixture. The greatest 

 difficulty is found in preventing extreme contraction of the speci- 

 mens. Stupefaction with chloretone resulted in contraction as 

 intense as that produced by the killing fluid : the use of hot 

 reagents was of some small advantage. Flattening between plates 

 of glass gave the least contraction, but had the disadvantage of 

 producing some distortion. The best results were obtained from 

 specimens killed in Zenker's fluid; the poorest from those killed 

 in Gilson's fluid. It is difficult to obtain good infiltration with 

 paraffine, especially in the normal (not flattened) specimens. 

 The modification of Apathy's method given by Lee was very 

 successful, leaving the tissues in good condition. High tempera- 

 tures (over 50 C.) are rapidly fatal to the integrity of the tis- 

 sues. The shortest possible time in paraffine of the lowest melting 

 point that can be used gives the most satisfactory result. 



The worm is very difficult to section because of the great 

 mass of eggs it contains. Various macerating agents were tried, 

 but none was of any great service. Sections were cut as thin as 

 4/x; most of the series ranged from 8/* to 16/*, the latter in col- 

 lodion. 



The stains used were : Heidenhain 's iron haematoxylin, 

 Benda's iron haematoxylin, Mayer's acid haemalum, Mallory's 

 connective tissue stain, Delafield's haematoxylin, Ehrlich's 

 haematoxylin, Lonnberg's borax carmine-Lyons blue, toluidin 

 blue. Iron haematoxylin preparations are excellent for the study 

 of cuticula, musculature and sex-cells; they are worthless for 

 the study of the nervous system and unreliable in many details. 

 No statements are based on results given by this stain alone. 



Mallory's connective tissue stain colored nervous tissue, with 

 the exception of the nuclei, bright blue. Its action was too 



