184 BULLETIN OF THE UNITED STATES FISH COMMJSSION. 



The specimens arrived in a living condition, and appeared perfectly 

 healthy, except that the gills and palps were discolored and had a dirty 

 blnish-green cast, which was in striking contrast with the color of these 

 parts in unaffected specimens. A better understanding of the parts in- 

 volved by this discoloration maybe had by reference to the accompanying 

 figure taken from Woodward's Manual of Conchology. The gills <j and 

 palps p 2> of the figure were the parts to which the discoloration was 

 confined. No other part of the tissues of the animals seemed to be in 

 the slightest degree affected. Fresh water seemed to have a tendency 

 1o bleach the gills when the animals were placed iu it for a time. Pre- 

 paratory to microtomical work upon the gills, the animals were first 

 killed in weak alcohol, then slowly hardened iu the same liquid, and 

 finally small fragments of the gills were put into absolute alcohol. Dur- 

 ing all of this treatment the gills lost but little of the color which per- 

 meated them. Subsequently the pieces which were to be cut into sec- 

 tions were saturated in clove-oil, then trans- 

 ferred to chloroform, which was changed 

 once, with still no evident loss of the color. 

 Tbc pieces of the gills were then heated in 

 a mixture of paraffine and chloroform to a 

 temperature of about 100° Fahr., without 

 destroying their coloration. The paraffine 

 and chloroform were finally replaced by 

 pure paraffine, in order that the objects 

 might be thoroughly saturated and the 

 more readily cut into thin sections. No 

 staining reagent was used, because it was 

 thought that tho coloration due to the 

 absorbed vegetable pigment would still be 

 evident in the sections. A foreign pigment 

 used to dye the sections would have viti- 

 ated the results and made it impossible for 

 one to see if one set of tissues had been 

 stained more deeply than another by the 

 color imbibed during life. The result 

 showed that there was but little difference 

 in the depth of the color of different layers. 

 The blood-cells seemed slightly darker in 

 color, but all of the tissues of these sec- 

 tions, which were cut iu a transverse direc- 

 tion, were more or less deeply stained and 

 of a dirty greenish color. 



No evidence of the existence of minute 

 parasitic animals or plants was observable either on the outside or in 

 the internal cavities of sections prepared from the gills. 

 My investigations have therefore led me to the conclusion that the 



