24 The MoUuscan Family Planorhidae 



Menettis sampsoni from slough of Meramec River east of Stanton, Franklin Co., 

 Missouri. Collected by Leslie Hubricht. Twelve out of fourteen specimens were in- 

 fested with cercariae, the liver and genitalia being principally affected. In several 

 specimens nearly all of the internal organs had been destroyed. 



Same species from small lake near Hutchins, Dallas Co., Texas, collected by 

 Dr. E. P. Cheatum. Fifty per cent of specimens examined were affected by cercariae. 



Promenetus exacuous from small lake in Wainwright Park, Alberta, Canada. Re- 

 ceived from A. LaRocque, Canadian National Museum, Ottawa. Nearly all specimens 

 examined were infested with cercariae, some in the fore part of the bod}', many about 

 the stomach, but mostly confined to the liver and genitalia. Specimens of exacuous 

 from Maine, Wisconsin, Michigan, New York, and Ontario did not contain larval 

 worms. 



It is unfortunate that parasitological assistance was not available when 

 these anatomical studies were in progress in order that the particular 

 species of parasitic trematode worms involved might have been ascertained. 

 Many species of cercariae remain to be discovered from the tissues of 

 planorbid and other fresh-water mollusks. 



The effect of fluke infestation on the anatomy of the snail is variable. 

 The cercariae may infest only the liver, in which case, often, the cercariae 

 finally leave the snail which recovers from the damage inflicted by the 

 parasite. In many other cases, however, the liver, genitalia, and stomach 

 are affected and in large measure destroyed. Specimens have been examined 

 in which the genitalia were completely destroyed or the genitalia and liver 

 obliterated. In one case (Menetus cooperi) , almost the whole snail was 

 so filled with cercariae (several thousand) that the normal organization 

 could not be distinguished, the cercariae being packed in the space occu- 

 pied by the organs and in aggregation taking their form. This was par- 

 ticularly true of the genitalia. Faust ( 1920, p. 79) has given a good 

 account of the pathological changes in the gastropod liver due to fluke 

 infestation. Wesenberg-Lund (1934) and ]\Iiriam Rothschild (1936) have 

 recorded instances of gigantism in snails apparently attributable to trema- 

 tode infections. 



Several parasitologists have essayed the role of conchologists in an 

 endeavor to understand the specific limitations of the groups of molluscan 

 species acting as hosts for i^arasitic trematode worms. Among these are 

 the late Dr. Adolpho Lutz (1918) of the Instituto Oswaldo Cruz and Dr. 

 A. Vianna Martins (1938) of the Laboratorio do Instituto Biologico 

 Ezequiel Dias. Dr. Lutz describes all species under the common generic 

 name Planorbis, the modern genera Australorbis and Tropicorbis being the 

 principal groups discussed. In the main, the work of Dr. Lutz is good and 

 the species have been carefully distinguished. The work of Dr. Martins is 

 a study of the genus Australoi'bis of Pilsbry, based in part on the earlier 

 work of Dr. Lutz. Unfortunately the two genera Tropicorbis and Austra- 

 lorbis have been confused by this author and many species lumped under 

 Australorbis, to which they have little relation anatomically. It is obvious 

 that specific identifications must be accurately made if any value is to be 

 attached to these forms as intermediate hosts of parasitic worms. 



In Part II of this work the recognized species, and also the synonyms, 

 of species of both Australorbis and Tropicorbis, as well as of other groups, 

 will be discussed and the species figured.* 



*The author's death came before he could finish Part II. However, 60 plates made 

 for Part II are printed as an Appendix to this work (see page 213 et seq.). H.E.C. 



