Parasitism in the Frog 205 



THE OCCURRENCE OF SECONDARY PARASITISM IN 



THE FROG. 



George Zebrowski, Purdue University. 



In a series of experiments on the life histories of certain Anuran 

 parasites, especially those of Rana pipiens, conducted under the direction 

 of Dr. H. E. Enders, several cases of secondary parasitism have been 

 observed, two of which are described in this 'article. 



By secondary parasitism is meant the occurrence of parasites in 

 forms which themselves lead an essentially parasitic existence. To the 

 uninitiated the mention of a parasite often brings to mind a few com- 

 mon forms such as the louse, the flea, the tick, or perhaps a tapeworm. 

 Unless one is actively engaged in the study of parasitology, it is difficult 

 to appreciate the tremendous number of parasitic forms that may be 

 found at one's very elbow. Indeed, it may be conservatively stated that 

 every animal, during its lifetime, is a host to one or more species of 

 parasites which are dependent upon it for their existence. 



This statement is prompted by a small, moribund, leopard frog, 

 which the writer recently dissected and which contained the following 

 astonishing list of parasites: 



Flatworms. 

 Pnewnonoeces coloradensis, in lungs, 5 



Loxogenes arcanum, encysted in musculature of stomach and in- 

 testine, 14 

 Clinostomes (sp.?), immature forms encysted generally, 137 

 Diplodiscus temperatus, in rectum, 5 

 Gorgoderina attenuata, in bladder, 3 



Roundworms. 

 Angiostouia nigrovenosiim, in lungs, 7 



Strongyh(s auvicularis (?), in intestine, 4 



Small, immature, active, free-living nematodes, (species?), in body 

 cavity, 17 



Protozoa. 

 Opalina, and Nyctotherus, several hundred in intestine and rectum. 



The infestation of parasitic forms by other parasites is a common 

 phenomenon, and especially is this true in the case of Protozoa. Thus, 

 the orders Flagellata, Gregarinida and Coccidiidea are replete with 

 parasitic species that may be dependent upon other parasites, commonly 

 insects, for their transfer to a final host. The Trypanosome of "sleeping- 

 sickness" and Plasmodium vivax, the causative agent of malaria, are 

 two of a number of well known examples which may be cited. It is 

 true that secondary parasitism among the higher metazoa is more diffi- 

 cult to find, but this is probably due to lack of research, rather than 

 to a lack of material. It is now definitely known that fleas are inter- 

 mediate hosts for larval stages of certain tapeworms. We have also good 

 reason to believe that other helminth forms can be transferred by in- 

 sects in this way. Doubtless this list could be further augmented, but 



"Proc. 38th Mcetins, 1922 (1923)." 



