45] PROTEOCEPHALIDAE — LA RUE 45 



have an important bearing on the proof of an identity. Frequently the 

 knowledge that two forms have the same species for a host furnishes 

 the first intimation that they may prove to be identical. 



One may also make the statement that the finding of specimens 

 apparently belonging to the same species in two or more unre- 

 lated host species may give an early intimation that these specimens 

 belong to different species. While it is true that certain cestodes seem 

 to be limited in their habitat to a single host species there is a sufficiently 

 large body of facts to warrant the belief that in general cestode species 

 are not so limited. It is of common acceptance that closely allied hosts 

 having a wide distribution and inhabiting the same regions and espe- 

 cially when they have similar feeding habits very frequently harbor 

 the same species of parasites. 



Gasterosteus aculcatus and G. pungitius are closely allied, have 

 Avide distribution, inhabit the same region, and have similar feeding 

 habits. Taenia ambigua has been reported from G. aculeatus by Grimm 

 and from G. pungitius by Dujardin and Schneider. Taenia filicollis 

 has been reported from G. aculeatus by Rudolphi, Goeze, Diesing, Du- 

 jardin, and Bellingham, and from G. pungitius by Diesing (from speci- 

 mens collected by Nitsch and Creplin) and Lonnberg. So far as hosts 

 are concerned there is evidence to believe that Taenia filicollis and Tae- 

 nia ambigua are identical species. Against this identity is the fact that 

 Dujardin 's description of T. filicollis indicates a larger form than does 

 his description of T. ambigua. It is a well-known fact, however, that 

 a considerable variation in length and breadth may exist in the same 

 species of cestode. These discrepancies in size may be due to the degree 

 of maturity and to the contraction states of the individual worms. It 

 is not known whether Dujardin 's specimens of T. ambigua had at- 

 tained their full development nor is this known concerning the speci- 

 mens described by Grimm or Schneider. There are no statements to 

 show whether Dujardin measured his specimens while alive or after 

 preservation. This would make a real difference. 



Attention has already been called to the fact that in regard to the 

 egg measurements made by Dujardin for the two forms in question 

 there is pretty good agreement. There is not sufficient evidence at hand 

 to prove positively that Taenia ambigua is identical with Taenia filicol- 

 lis, yet it seems that the evidence for the identity is stronger than the 

 evidence against it. Therefore in this work the writer will consider that 

 these species are identical and since Taenia filicollis has the right of 

 priority that name should be retained. It is to be hoped that this dis- 

 cussion, which in no way can be considered to settle the problem of the 

 identity of these species, will be the incitement to a genuine compara- 



