422 University of California Publications in Zoology. [Vol. t> 



the posterior end. In the Cestodaria, conflicting views as to the 

 orientation of the various genera have long existed, and in the 

 genus Gyrocotyle the question never has been conclusively 

 settled. It is of peculiar importance for the problem of cestode 

 orientation in general that these relations should be well estab- 

 lished in Gyrocotyh , for there is no functional antero-posterior 

 orientation in the adult merozoic cestode and the problem there 

 is one of comparative morphology and phylogenetic develop- 

 ment. Since Gyrocotyle is in every respect a primitive, rela- 

 tively simple form, parasitic in one of the must ancient of 

 vertebrates, it seems reasonable to assume that this cestode may 

 give some hint as to the extremity at which the ancestral cestode 

 most probably developed its organ of firm attachment. Observa- 

 tions of the living animal have shown that in Gyrocotyle there 

 is still a definite functional antero-posterior orientation, due to 

 the fact that it is not a permanently attached form but is still 

 capable of locomotion. 



Diesing (1855) regarded the acetabular end of Gyrocotyh 

 as anterior, but his grounds for this decision are not clear. 

 Working with a few poorly preserved specimens, he had little 

 on which to base his conclusions. Wagener (1852), who did 

 careful work on the living animal and on sections, had proposed 

 the same orientation on the basis of the active exploring move- 

 ments of the acetabulum in the living animal, ami of the loca- 

 tion of a bridge commissure of the central nervous system at the 

 base of the acetabulum. This orientation was followed by suc- 

 ceeding investigators up to Spencer (1889), who reversed it on 

 the strength of the discovery of a similar and much heavier bow- 

 commissure at the rosette extremity. He did not observe living 

 material. Lonnberg, working on a large quantity of living and 

 preserved material, followed Spencer in regarding the rosette as 

 anterior, basing this decision on the behavior of the living animal 

 (the stretching out of the rosette and funnel into a long canal 

 which performed exploring movements and is directed forward 

 in locomotion, according to his observation), on the great de- 

 velopment of its nervous system in the funnel region, and the 

 greater abundance of ganglionic cells in that as compared with 

 the acetabular commissure, on the direction of the spinules. 



