DISTRIBUTION OF CLINOSTOMUM MARGINATUM. 353 



that we are not in possession of a particle of information regarding 

 the early stages of its life-history. The worm is fully developed 

 when it is encountered in the fish or frog and all that' is needed 

 for its complete maturity is that the vitellaria shall become 

 active, which they do as soon as the parasite reaches the 

 heron. The details of structure of the worms of the bass have 

 been determined both in total preparations and in serial sections. 

 In the smallest individuals the entire organization is developed. 

 It follows from this fact that there are three hosts involved in the 

 life-history of this species of which the fish or frog is the second 

 and the heron the final one, the first being unknown. The role 

 of the fish or frog does not appear to be one of importance from 

 the view point of the ontogeny, but seems merely to be for the 

 purpose of getting the w T orm to the heron. It thus would appear 

 that the primary host is not one which serves as food to the heron 

 but does serve as food for the bass. This would fit the case of 

 insects as well as any group of invertebrates. 



In view of the fact that this parasite infects the edible portion 

 of such important game and food fishes a knowledge of its life 

 history is particularly desirable. While the parasite is fortu- 

 nately one which is not injurious to the human system, at the 

 same time its presence in the bass and perch unfit them for the 

 table. It is clear that the worm is already widely distributed 

 and is a menace to fish-culture, which at any time may become 

 of great importance. It seems likely that if one were able to 

 take up the problem of this life-history under favorable con- 

 ditions for instance at some small body of water where the 

 infected fish were abundant and to follow it up at various seasons 

 the missing data could be obtained. 



The data given in the foregoing paragraphs are summarized 

 in the following table. 



