SHORTER ARTICLES AND DISCUSSION 



A BIOLOGICAL SURVEY OF DESCRIBED CERCARI^ 

 IN THE UNITED STATES* 



Among the earlier American zoologists Joseph Leidy alone 

 was a student of cercaria?. From his time to very recent years 

 American cercarife have received little attention. This may 

 have been due to the greater demands made by other groups of 

 animals, or possibly to the minute size of the larvae and a failure 

 to appreciate the exact differences of their structure. It could 

 not have been due to a lack of knowledge of the presence of cer- 

 cariae, for the European records were abundant and the classical 

 studies of Leuckart, Ercolani and Looss had demonstrated the 

 life-history relations of cercariffi and adult flukes. Moreover, 

 the large number of adult trematode records showed that the 

 larvas must be fairly abundant. 



Within the past few years a revival of study in this larval 

 group has revealed a large number of forms, so that now there 

 are some sixty named species. Only eight of these have dates 

 prior to 1914. The majority of described eercariae have been 

 worked over by Cort, Faust and O Rokc 



A study of the descriptions of carlifr nailed species shows 

 them to be very general, so that they a|){)ly not to the species at 

 all but to larger groups, genera or i)erliaps even subfamilies. 

 For example, the record of a monostome with three eye-spots 

 instead of characterizing a species merely distinguishes the tri- 

 oculate from the binoculate group of species. A parallel is 

 found in the diplostomulum commonly known as Diplostomum 

 cuticul<h von Nordmann 1832, which has been recorded from a 

 variety of vertebrate hosts and from equally variable habitats. 

 There is great probability of the existence of several new spe- 

 cies concealed beneath these generalized data. Such cases illus- 

 trate the futility of generalized descriptions. 



Cort emphasizes the value of the excretory system of the cer- 

 caria as a basis of description. The conservatism of the system 

 is urged as a basis on which fundamental groui) rt'lationshi[)s 

 of the trematodes can be discovered. Advaiitajre in usinu^ this 



Illinois, No. 113. 



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