317] PSEUDOPHYLLIDEA FROM FISHES— COOPER 29 



line, from which a straight portion passes ventrally thru the musculature and 

 cortex to the opening which is about 20/i in diameter (35^, Linstow). The 

 diameter of the duct is 60ju in the median frontal plane but only half that 

 amount as it passes thru the longitudinal muscles. The measurements of the 

 eggs are according to Kiessling and Linstow, respectively, 49 by 34ju and 65 by 

 42ju : they were found by the writer to be 50 to 54 by 30 to 33n in sections. 



Our knowledge of the life-history of the species is confined chiefly to the 

 works of Duchamp (1876), Donnadieu (1877) and Riehm (1882) who firmly 

 established the well-known fact that the larva present in the abdominal cavities 

 of various species of teleosts develops rapidly in the intestines of fish-eating 

 birds. The production of eggs begins after about 36 hours, while the adults 

 live for from three to four days only in the definitive hosts. Apart, however, 

 from these and other closely related details which were brought out by Donn- 

 adieu by means of well conducted and controlled experiments, nothing is 

 known, so far as the writer is aware, of the development of the oncosphere in 

 the intermediate host up to the time when it becomes distinguishable as 

 a small larva. The measurements of the smallest larva found in connection 

 with this study have been given above; another slightly larger specimen 

 was 6.1mm. in length by 1.34mm. maximum breadth. 



Altho the above description shows many discrepancies between the species 

 as here dealt with and the European form, the writer does not feel justified in 

 separating the two specifically, especially in the absence of European material 

 for comparison. The thickness of the cuticula, and subcuticula, the dimen- 

 sions of the testes, seminal vesicle and cirrus-sac and the diameter of the 

 vagina show the greatest differences, apart from the probable confusion by 

 Linstow of the oocapt and receptaculum seminis, while the measurements of 

 the eggs as here given are somewhat intermediate between those by Kiessling 

 and Linstow. But the fact that the data given by the latter are apparently 

 the only adequate ones for the adult and that there are not a few discrepancies 

 between KiessUng's and Linstow's accounts restrains one from looking upon 

 this, the American form, as new. In dealing with this question of identity 

 it must also be remembered that not only does the species vary so much that, 

 as pointed out above, a great deal of confusion exists in the earlier literature, 

 but that the number of host species of the larva as well as of the adult is very 

 large as compared to other species of bothriocephaUds, hence introducing 

 greater factors for variation. And above all the geographical distribution of 

 the wading and diving birds harboring the mature worms is such that here in 

 America there are many of the same species as well as the same genera that 

 occur in Europe. As the above record of hosts indicates, the species certainly 

 ranges widely over Europe and Northern Asia, so that it would be quite sur- 

 prising if it did not occur here in North America, with the probable region 

 of transition in Iceland and Greenland on the east and northeastern Siberia 

 and Alaska on the west. However apart from Leidy's and Linton's records it 

 has apparently not been reported up to the present. 



