356 University of California Publications in Zoology. L VoL - 6 



much simpler, and that its structure and position afford very 

 significant indications of the origin and primitive location of the 

 cestode scolex. The evidence of this homology and its theoretical 

 significance will be discussed later; the point of chief interest 

 now is that the very structural peculiarity which Lonnberg 

 regarded as removing Gyrocotyle from any great phylogenetic 

 interest is the source of its most significant and interesting 

 contribution to the solution of the problem of cestode origins. 



This investigation has been carried on in the Zoological Labo- 

 ratory of the University of California and at the Station of the 

 Marine Biological Association at La Jolla. For material I am 

 indebted to Professor C. A. Kofoid, and through him to the 

 United States Bureau of Fisheries and the Marine Biological 

 Association at La Jolla ; also to Professor Jacques Loeb, for 

 privileges at the Herzstein Research Laboratory at Monterey. 

 For substantial assistance in the preparation of drawings for 

 publication I am indebted to Miss E. J. Rigden. For the point- 

 ing out of this line of investigation, for help in obtaining the 

 obscure and not easily accessible literature of the subject, and 

 for counsel and encouragement, I wish to express my debt to 

 Professor Kofoid, under whose direction this work has been 

 brought to its present state of completion. 



B. HISTORY OF THE GENUS. 



The history of the genus Gyrocotyle is complicated by con- 

 flicting reports as to its systematic position, its habitat, its orien- 

 tation and its morphology. The genus was established by 

 Diesing (1850), for a parasite obtained by Gueinzius in 1842 

 from Ant il a/ a pygarga, a South African ungulate. This report 

 was an error (Diesing, 1858, p. 492), but was accepted as correct 

 for several years, contributing in no small degree to the confusion 

 concerning the habitat and systematic position of the genus. In 

 1S44 Kroyer showed Diesing a parasite similar to that collected 

 by Gueinzius. taken from inside the shell of an edible mollusk 

 (Diesing, 1855). These two specimens were grouped in one 

 species by Diesing (1850) under the new genus Gyrocotyle, and 

 described in the following terms: 



