34 ILLINOIS BIOLOGICAL MONOGRAPHS [322 



Adult stage: Alca pica, Ardea cinerea, Ciconia ciconia, C. nigra, Colymbus 

 arcticus, C. cristatus, C. glacialis, C. griseigena, C. immer, C. troile, Corvus 

 corax, Larus argentaius, L. capistranus, L. marinus, Mergus alheUus, Mergus 

 merganser, Podiceps cristatus, P. rubricollis, Sterna arctica, S. macroura, S. minuta, 

 S. nigra and Uria grylle. 



As indicated in the above synonymy this species was known for ahnost a 

 century, at first as the larval form only and then as both larval and 

 adult forms, before it was discovered that the two species recognized 

 from the time of Bloch (1782) were one and the same. Abildgaard (1790), 

 who called the worm T. gasterostei, seems to have been the first to consider the 

 larval form foimd chiefly in sticklebacks to be the same as that found in fish- 

 eating birds, since on feeding sticklebacks infected with the larvae to geese 

 he obtained the adult form from the intestines of the latter. Yet Rudolphi 

 (1810) did not agree with his conclusions but still considered that there were 

 two distinct species, namely, Bothriocephalus nodosus (adult) and B. solidus 

 (larva). And this continued until Creplin (1829) united both in one species 

 under a new genus, Schistocephalus dimorphus. Diesing (1863:233) made a 

 new species out of the Schistocephalus found by Weinland (1859) in the island 

 of Hayti in Rhynchichthys gronovii, but later writers have considered that in 

 all probability it was only the well known larval form of this species. Wille- 

 moes-Suhm (1869) was evidently the first to study the development of the 

 fertilized oviun, which was later gone into more thoroughly by Schauinsland 

 (1885:555). Donnadieu (1877), to whom all go back in their considerations 

 of the larval development of Ligula, unfortunately fell into the error of con- 

 sidering Schistocephalus and Ligula to be not only the same specifically but 

 generically. The anatomy ^\'as first studied by Moniez (1881:175), more 

 thoroughly by Kiessling (1882), and still later by Furhmann (1896) (under B. 

 zschokkei sp. nov.) and Solowiow (1911). Linton (1897:427) is the only one, 

 apart from Weinland's record which is only a brief foot note, who has 

 reported the species from America. 



As regards the correct name of the species, it should be noted that, altho 

 Liihe (1899:52) called the "typical and only species" of the genus Sch. nodosus 

 (Rud.) and the larval stage Sch. solidus (O. F. Mliller), he reverted in 1910 

 to "Schist, gasterostei {Fabr.) ( = Sch. dimorphus Crepl.)" without, however, 

 discussing the change. But according to the Rules of Nomenclature, Art. 

 27 (b), the earliest name of the larval stage must hold, so that, since Liihe 

 himself considered this to be Sch. solidus (O. F. Miiller), the writer makes 

 use of the latter in the present paper. 



According to Luhe (1910:19) Sch. solidus ranges in length from 30 to 300mm. 

 while the maximum breadth varies from about 3 to 9mm. and is located ahead 

 of the middle of the strobila. As shown in the table below the largest and only 

 sexually mature specimen of the six studied by the writer was only 29mm. in 

 length by 6mm. in breadth. The scolex (Fig. 3) is, as indicated in the above 

 diagnosis of the subfamily, not separated from the first segment into which it 

 runs insensibly, the whole " head " being thus triangular in shape. The bothria 



