Linton. — Trematode Parasites of Fish 251 



(1911) also reports this distome from a heron sent to him 

 from Nebish, Mich. Although the bird had been dead a day 

 or two, he found the worms still alive in considerable num- 

 bers adhering to the wall of the throat by means of the 

 anterior end used as a sucker. 



Upon comparing the distome from the flesh of the trout 

 with published figures and descriptions of this adult form 

 from the bittern and the heron it is evident that they are one 

 and the same species. 



Since it is possible to identify the species with such a 

 degree of confidence, we are furnished with a clue to the 

 source of infection of the trout of Alder Lake. Heron are 

 not infrequent visitors at the lake, and the distomes now in- 

 festing the flesh of the trout in these waters, with little 

 doubt, owe their existence to eggs which were introduced 

 into the waters of the lake along with the excreta of some in- 

 fected heron or herons which have visited the lake sometime 

 within the past year or two. It should be stated that the 

 worms were first observed in the flesh of the trout by Mr. 

 L. F. Bliss, steward of Mr. S. D. Coykendall, the owner 

 of the preserve upon which the lake is situated, in the au- 

 tumn of 1910. 



Trout are, as a rule, exceptionally free from parasites in 

 the flesh. It is therefore worth while in a paper of this kind 

 to consider the reasons for the exceptional occurrence <>l" 

 this distome in the trout of Alder Lake. It is to be noted 

 that while the conditions under which the trout are living 

 in this lake are not unnatural they are unusual. The level 

 of the lake has been raised by a dam at the outlet over 

 which trout cannot make their way from the stream below. 

 To find a similar condition in nature where fish are living 

 in a lake to which they are confined, that is, where they can- 

 not move freely to and from the lake by means of the outlet, 

 one must go to such a lake as Yellowstone Lake. It is of 

 interest to note that in that lake the trout are likewise in- 

 fested with a parasite in the flesh, and that the parasite is 

 an immature cestode worm which reaches its adult stage in a 



