360 HENRY LESLIE OSBORN. 



form of this pose too is only momentary, and no preserved speci- 

 mens show it. In all cross sections of the worm the body is 

 elliptical and has a thickness of nearly half its breadth. 



The transverse parenchyma muscles are the ones which are 

 used in the swimming pose, the longitudinal muslces being at 

 rest. Alternate contractions of the transverse and longitudinal 

 muscles would throw the animal first into one, then into the other 

 of these positions. The observation of certain leeches furnished 

 the suggestion for calling this the swimming pose. In the leeches 

 the margins of the body are thinned in this way and reduced to a 







thin lateral fin and the worms swim rapidly through the water. 

 In the specimens of Clinistomum which were under observation 

 no vibrations of the body were made and the pose was not turned 

 to any account. It is possible that in nature this body form 

 would be adapted to progression through the chyle and chyme 

 of the bird and would be the means by which the worm reaches 

 the throat toward which it is travelling from the stomach or 

 intestine. It w r ould be very interesting to experiment with 

 these worms by removing them from cysts and placing them on 

 surfaces as much like the avian mucous membranes as possible 

 so as to ascertain whether these poses are as adaptive as they 

 seem to be. 



4. ON THE CYSTS IN THE FROG. 



The first mention of the frog as a host of Clinostomum is by Mac- 

 Callum ('99), who reports it from the pectoral muscles of frogs 

 found in Ontario. We have been finding it now for several years 

 in the frogs caught in the vicinity of St. Paul which are used in 

 our biological courses. 1 The mode of infection of the frog is 

 different from that of the bass. The cysts, instead of being 

 located in the muscular tissue, are seldom found there, but are 

 in the peritoneal lining of the ccelom or in the lymph spaces 

 between the skin and the muscles of various parts. Text-figure I 

 is drawn from the most considerably infected specimen which 

 I have met. The cysts are located in the ccelomic cavity; 



1 It is most probable that frogs and fishes in many parts of this country are in- 

 fected by this parasite. Any information as to localities elsewhere where it has 

 been noticed would be very gratefully received by the writer. A study of the re- 

 lation of the worm to the frog is now in progress, and it is hoped that clues to the 

 early history of the worm may be obtained through its connection with the frog. 



