MUSSEL FAUNA OF MAUMEE RIVER. 



67 



Anodonta cygnea of Europe; hence a few remarks concerning it may 

 not be out of place. 



So far D. duplicatum has not been reported from any mussels ex- 

 cept Anodonta, Its discoverer found it usually in the kidneys of 

 Anodonta ventricosa and more rarely in the same organs in A, ana- 

 tlm. One badly infected example of this latter species had the 

 sporocysts in the kidneys, gills, pericardial cavity, and edge of the 

 mantle, and in an example of A. ventricosa they were even present in 

 the general circulation. Filippi found the sporocysts and free dis- 

 tomids in the mantle of A. cygnea^ some of them surrounded by nacre ; 

 and Pagenstecher found them in the tissue of the genital glands, 

 liver, and kidneys of the same species. In this country Leidy ^ has 

 reported '''Rhophaloceixa tardigrada attached to the mantle of Ano- 

 donta -jiwinatilis; specimens also obtained by Mr. Lea from A. 

 lacustrisy 



The mature form of Distomum duplicatum is said to be D. tereti- 

 colle Rudolphi, a parasite of fresh-water fishes. 



To return to the distomid of Osborn: In addition to its being 

 found in Anodonta grandis^ this parasite (in the distomid form) has 

 also been reported from Stro'phitus edentidus by Osborn. We had 

 very few living mussels of this species to examine; however, we 

 found dead shells with the peculiar salmon-colored nacre, similar to 

 that produced by this parasite in Anodonta. 



In view of the fact that a Distomum quite similar in appearance 

 to this is found in other species of mussels, while sporocysts are rare 

 (we found them only in the liver tissue of one example of Quadrulo. 

 tuberculata in Tippecanoe Eiver), it becomes an interesting ques- 

 tion whether this distomid migrates from the Anodonta to other 

 mussels after issuing from the sporocyst. In the first place, such a 

 migration is probably not an event closely connected with the life 

 history of the species; for the tail, which functions as an organ of 

 locomotion in those species which do migrate, has here been allowed 

 to become functionless, or even a dead weight. Moreover, if the host 

 of the mature form is a fish, as one might expect it to be from the 

 life history of its near relative D. duplicatum^ it would be to the 

 advantage of the distomid to remain in the thin-shelled Anodonta^ 

 which is much more likely to fall a prey to fishes, or indeed any 

 other predaceous animal, than the thicker- shelled species of mussels. 

 It is very likely, however, that, just as in greatly infested mussels 

 the cercarise frequently overflow the organs which appear to be their 

 favorite habitat, so a considerable number of distomids may be 

 crowded out of the host mussel and be forced to seek protection and 

 food elsewhere. According to von Baer ^ the sporocysts of Distomum 



« Proceedings of the Academy Natural Sciences, Philadelpliia, 1858, p. 110. 

 ^ Loc. cit. 



