No. 6.] PARASITISM OF ANODONTA PLANA LEA. 307 



with much color and no flukes ; these cases have not been 

 numerous. I have interpreted them to mean that the flukes 

 have migrated in search of another host. 



The constant occurrence of the flukes in correlation with 

 the coloration seems to be sufficient evidence to justify the 

 conclusion that they are the cause of the coloration, but when 

 one attempts to go beyond this point and determine the exact 

 relation that exists, one reaches a realm of speculation. It 

 seems to me probable that the red color is a modification of 

 the secretion of the mantle due to the irritation by the flukes. 

 I have not been able to find out why the flukes collect as they 

 do, and am inclined to suppose some attraction, perhaps of 

 food, which draws them to the points where they are habitually 

 found. 



IV. FACTS ABOUT THE PARASITES. 



The parasites present some points that are of interest to the 

 student of the trematodes. Many specimens were examined 

 alive under compression, and many others were studied in total 

 preparation of specimens that had been fixed in corrosive 

 sublimate solution and carried up through the alcohols and 

 cedar oil to Canada balsam. One specimen was sectioned 

 serially and the series carefully studied ; the following descrip- 

 tion rests on these three modes of study. 



A view showing the points observed on the living specimen 







and on the total preparation is shown in Figs. 3 and 4. The 

 total length of the body in the living fluke was variable, accord- 

 ing to its state of contraction, and it presented every condition 

 between a broad and short form and a very long and slender 

 one. The length of the preserved specimens is .04 of an inch. 

 A living specimen under slight compression from the weight of 

 the cover glass measured .054 inches. 



All the structural features of the parasite are indicated in 

 the accompanying text-figures, so that only a brief mention of 

 them is necessary. The outline of the body is broadly ellipti- 

 cal and there is no distinction into regions. The outer skin is 

 everywhere, except the suckers, entirely simple, and I did not 

 see any conspicuous cuticle ; there are no spines of any kind 

 visible in any portion of the skin. 



