Linton. — -Trematode Parasites of Fish 253 



the back and stripping away the skin a few black pigment 

 spots were found similar to those on the fins. Some of these, 

 being in the dermis, adhered to the skin, others were in the 

 muscle tissue although none of them lay deep in the muscles. 

 All of them could be seen on the side of the muscle mass 

 that had been next the skin. These pigment spots were 

 rather more abundant along the back and on the posterior 

 half of the body of the smaller fish, although they were 

 also found in the muscles near the gill opening and in the 

 pectoral muscles. About 53 were found in the flesh, and a 

 few on the gill arches. In the larger fish the distribution 

 was much as it was in the smaller specimen. There were 

 about 30 cysts, mainly on the sides in the middle region, one 

 being found in the muscles at the depth of 4 millimeters. 

 Each cyst that was examined contained a larval trematode. 

 So far as they were studied they were found to suggest the 

 form described by Leidy under the name Diplostomiim 

 gracile, although one of them which was removed from the 

 cyst and stained and mounted in balsam was thought to sug- 

 gest the genus Holostomum. 



In July, 1905, I spent one day at Alder Lake examining 

 the brook trout for skin parasites. A description of condi- 

 tions as they then existed has already been published ( Inter- 

 national Zoological Congress, 1907). While none of the 

 trout had large numbers of cysts in the skin a large propor- 

 tion of them were infected. A few 7 had as many as 20 or 30 

 cysts visible on one side, some had none, others had from 

 1 to 5 on one side. Upon that occasion the owner was ad- 

 vised to discourage the visits of fish-eating birds to the lake 

 as much as possible. This advice was followed. Upon my 

 visit to Alder Lake this summer, after an interval of six 

 years, I found the skin parasites of the trout less prevalent 

 than they were in 1905. Of the 70 fish examined nearly 

 half were without any cysts whatever. 



I was not able to refer the larval distomes found in 1905 

 in these trout with certainty to any genus with which I was 

 acquainted, although the genus Diplostomiim was suggested. 



