PROTEOCEPHALUS AMBLOPLITIS LEIDY 191 



SESSIONAL PAPER No. 39b 



the early stages of the Ichthyotaeniae almost nothing has yet been published." 

 Schwarz ('08), in speaking of the development of the reptilian Ichthyotaeniae, takes 

 Gruber's observations as his basis and proceeds to elucidate the infection of rep- 

 tiles through Cyclops and the aquatic habits of the hosts concerned. Fuhrmann 

 ('03) considers the larvae found in the livers of Salmonids and Percids by von 

 Linstow, von Siebold and Zschokke as strayed larvae having mistaken hosts and 

 having then taken a particular aspect. This view would explain the fate of num- 

 bers of the plerocercoids of P. ambloplitis found encysted in young and old bass. 

 Unless the bass were eaten by larger fish such as Amia, Lepisosteus, Esox or 

 Salvelinus in which they could develop as in a second final host they would surely 

 disintegrate eventually. Fuhrmann showed by his infection experiments that 

 the intermediate hosts of the Ichthyotaeniae were the one or the other of the cope- 

 pods found in the plankton used as food. LaRue's infection experiments with 

 Chironomvs larvae, Daphnia, Cyclops, Notonecta, some larvae of the Dytiscidae, 

 tadpoles of Rana catesbiana, besides the Salamander {Amblystyma tigrinum) 

 itself proved failures as -did those of Schneider ('04). However, he furnishes 

 conclusive evidence, "first, that the encysted plerocercoid (of P. filaroides) is 

 the larval form of the cestode found in the same host; second, that the period 

 of development from the plerocercoid after ingestion is short." 



In connection with the present study only a few infection experiments were 

 tried, but they gave no results; it was found very difficult to keep the young of 

 M. dolomieu alive and unmolested, — they are very sensitive to change of environ- 

 ment — whereas the young of M. salmoides are easily kept in captivity. However, 

 a thorough series of dissections was carried out with bass of all sizes from those 

 taking their first food after hatching, about 8 mm. in length, to adults. This 

 resulted in a very fair acquaintance with the great variety of food-forms of M. 

 dolomieu as found on the eastern shore of Georgian Bay, but the points elucidating 

 the life-history of P. ambloplitis were rather few in number. 



Plerocercoids were first found in hosts about 40 mm. in length and between 

 that and 50 mm. the infection was not considerable. The organs infected were, 

 first the liver, then the alimentary tract and coelome. Observations on methods 

 of infection pointed, first, to the direct development of the oncospheres accidentally 

 introduced (autoinf ection) , their subsequent transference by means of the blood 

 stream (Braun), and the boring of the oncospheres themselves; second, to infection 

 from invertebrate food-forms such as Sida, Daphnia, Chironomus larvae and Coriza; 

 and thirdly, to infection from minnows and young perch which constitute a part 

 of the food and from which large numbers of very small plerocercoids closely 

 resembling the youngest stages described above are freed in the stomachs of the 

 bass. This latter method is borne out by the fact that no tape-worms were found 

 in those fish examined in the early fall of 1910 when the food taken was composed 

 wholly of crayfish, whereas a co^lparatively heavy infection was found with those 

 taken on the outlying reefs and islands where minnows constitute the bulk of the 

 food. Thus the evidence points to P. ambloplitis having at least two intermediate 

 hosts, the first, some unknown species of aquatic arthropod, and the second, either 

 different species of minnows, small perch or the final host itself. 



