306 OSBORN. [VOL. I. 



nacreous luster of the shell over the points of red coloration, 

 and they indicate, not a separate layer of red deposited on the 

 nacre, but the secretion of some soluble material which is 

 poured out with the nacreous secretion and hardened with it. 



III. RELATION OF THE PARASITES TO THE SHELL. 



The parasites concerned in the red coloration are found 

 attached by their suckers to that surface of the mantle which 

 is toward the shell. Their home is thus in a perfectly closed 

 chamber out of direct contact with the water, which is the 

 home of the host and remote from sources of food such as are 

 usual to parasites of their kind. Though I have carefully 

 searched for them in other portions of the Anodontas, I have 

 never been able to discover any in any other part of the host. 

 I have not been able to find any evidence to show that the 

 parasites enter the host with the in-going water and then bore 

 through the tissues to find their place of residence. I have 

 examined the surface of the mantle carefully to find any modi- 

 fication which its surface might have undergone, but without 

 finding anything that could be assigned to the flukes. I have 

 also sectionized the mantle for indications of flukes, but have 

 not found any traces of them there. I am, therefore, inclined 

 to believe that they reach their home by inserting themselves 

 at the margin between the shell and the mantle. 



The parasites are found in the red-colored shells almost with- 

 out exception, and are always found directly at the points of 

 coloration. In some cases there are a very few flukes, and 

 these are umbonal in position or there is a line of them in the 

 anterior line of coloration. Usually in shells with much color 

 there are a great many flukes, and generally the flukes are 

 found to agree in number and position with the red. I 

 have found some highly colored shells in which there were no 

 flukes, and concluded that they had migrated. I have also 

 examined shells in which there was no coloration without find- 

 ing any flukes. So that it can be said that the flukes are 

 constantly present in colored shells, and that they are located 

 at the points of coloration. I have found a very few shells 



