266 H. J. VAN CLEAVE 



S. Lemnisci 



These unique structures, while extremely simple in organiza- 

 tion, have been the subject of considerable speculation among 

 writers dealing with the genus Eorhynchus. Saefftigen ('84, p. 9) 

 recorded two nuclei in each lemniscus of Eo. rutili (Mtill.). Ha- 

 mann ('91, p. 140) corroborated this for the same species and later 

 ('95, p. 30), described the same condition for the only other then 

 known species of the genus, Eo. agihs (Rud.) . He mentioned an 

 instance of an immature form of Eo. rutili in which only one 

 nucleus was present in each lemniscus, while the second nucleus 

 was just in the process of formation. He says, ''Ein junger 

 Echinorhynchus clavaeceps, der mir vorliegt, zeigt gering ent- 

 wickelte Lemnisken, die aber bereits den einen Kern enthalten, 

 wahrend der andere noch an der Grenze ihrer Entstehung liegt." 

 This condition finds ready explanation in the light of facts brought 

 out later in this article. Still more recently Liihe ('11, p. 12) 

 recorded two nuclei in each lemniscus of Eo. rutili. His figure 1, 

 copied here as figure 31, shows but a single nucleus in each 

 lemniscus. 



It seems hardly necessary to mention that these observations 

 as given by various writers on the Acanthocephala add nothing 

 to the direct evidence for or against the problem of cell constancy. 

 However, they do serve to indicate the ease with which one may 

 be led to accept the assertion of an earlier worker without fully fol- 

 lowing out the evidence upon which his statements are founded. 

 To one working on a pm'ely anatomical problem it is extremely 

 plausible to decide that a form is immature when only a single 

 nucleus appears where others say two should occur. Such seems 

 to have been the condition when Hamann reported this abnor- 

 mahty, but, in the light of the present study of the structure of 

 the lemnisci of the numerous examples of Eorhynchi, it is difficult 

 to see the source of this evidence of a second nucleus just at the 

 beginning of its formation. All the facts gained from the study 

 of five species of this genus point to a condition mentioned by 

 none of these previous investigators, namely, while one lemniscus 

 possesses the two nuclei so generally ascribed to each, the other 



