SEASONAL INFECTIONS 207 



TABLE II 



Frequency of Double Infections 



Species Frequency 



Euhaplorch'ts californiensis + Y-bladder cercarla. 158 



Eultaplorcliis californiensis -\- small strigeld cercaria 87 



Small xiphidiocercaria -\- Y-bladder cercaria 76 



small strigeid -\- Y-bladder cercaria 55 



small strigeid -\- large xiphidiocercaria 45 



Y-bladder cercaria + large xiphidiocercaria 43 



Catatropis sp. -\- small xiphidiocercaria 32 



E. californiensis -\- schistosome cercaria 28 



small strigeid -|- small xiphidiocercaria 22 



Catatropis sp. -f- large xiphidiocercaria 15 



Y-bladder cercaria -j- unidentified 14 



Parastictodora hancocki -f- small strigeid 10 



schistosome + Y-bladder cercaria 8 



Catatropis sp. -|- Y-bladder cercaria 7 



P. hancocki -f- Y-bladder cercaria — - 7 



fin-tailed echinostome -\- schistosome 7 



Phocitremoides ovale + Y-bladder cercaria 6 



Cercaria buchanani -\- E. californiensis 6 



large pigmented echinostome -\- schistosome 4 



large xiphidiocercaria -(- schistosome 4 



Catatropis sp. + unidentified 3 



Catatropis sp. -f- small strigeid 3 



schistosome -\- P. hancocki _ 3 



large pigmented echinostome + E. californiensis 3 



P. hancocki -j- small strigeid 2 



Catatropis sp. -\- E. californiensis 2 



schistosome + small strigeid 2 



C. buchanani -\- large xiphidiocercaria 2 



C. buchanani -|- small xiphidiocercaria 2 



C. buchanani -f- small strigeid 2 



large pigmented echinostome -\- Y-bladder cercaria 2 



schistosome + small echinostome 1 



schistosome + small xiphidiocercaria 1 



E. californiensis -\- unidentified 1 



Y-bladder cercaria -f- unidentified 1 



Y-bladder cercaria -\- P. hancocki 1 



Y-bladder cercaria -\- fin-tailed echinostome 1 



small strigeid + unidentified 1 



667 



Purely on a basis of chance, double infections involving species with 

 the higher infection numbers should occur most frequently. However, 

 this was not always the case as is shown by the following frequencies of 

 double infections for the top seven species listed in Table I. The Y-blad- 

 der cercaria, although fourth in total number of infections, occurred most 

 frequently in double infections (373 times). Euhaplorchis californiensis 

 was second with 282, the small strigeid third with 207, the small xiphidio- 

 cercaria fourth with 133, the large xiphidiocercaria fifth with 109, Para- 

 stictodora hancocki sixth with 23, and large pigmented echinostome sev- 

 enth with 9. Proceeding down the list of species in Table I to Catatropis 

 sp., schistosome cercaria, and Cercaria buchanani, we find the respective 



