THE BEHAVIOR OF A PARASITIC COPEPOD 55 



ually increased, the motion of the copepods became slower, 

 until death finally overtook them in the lighted side of the 

 dish. The organisms are so strongly positive in their reaction 

 to light, that they persist in going toward the source of greatest 

 illumination, even though they are brought into regions that are 

 dangerous to their existence. 



X. INFECTION EXPERIMENTS 



In the hatchery ponds, as well as in the natural streams 

 Lernaeopoda edwardsii was found to attack the brook trout 

 only. A great many rainbow trout as well as German-brown 

 trout were examined and not a single case of infection by the 

 copepod was observed. Furthermore, suckers that were kept 

 in the hatchery ponds, as well as those thriving in neighboring 

 trout streams were examined, but were found to be clean and 

 healthy. Now the question arose: What explanation could 

 be offered for this choice on the part of the copepod for the 

 brook trout only? In attempting to determine this a series 

 of infection experiments were undertaken. 



Three groups of three copepods were placed into three sepa- 

 rate dishes of water. Into each dish was then placed, respec- 

 tively, the gills of freshly killed brook, rainbow and German- 

 brown trout. The fresh blood of the gills soon began to diffuse 

 in the water and the behavior of the copepods was noticed. 

 The copepods in the first dish into which the gill of the brook 

 trout was thrown, became very active, darting about in every 

 direction, as if they were in search of something. In the other 

 two dishes, which contained the gills of the rainbow and German- 

 brown trout, no such reactions of the copepods were noticeable. 

 Two of the animals came in contact with the brook trout gill 

 and began to attach themselves. In the other two dishes no 

 attachment took place, in spite of the fact that the organisms 

 came in contact with the gills a number of times. 



The manner in which the copepod attaches itself to the gills 

 of the brook trout is very interesting. Wilson (191 1), in his 

 paper on the development of Achtheres amblophitis Kellicott, a 

 copepod of the family Lernaeopodidae, parasitic on trie gills of 

 the rock bass, describes the attachment of the organism as 

 follows: "Of course, it is practically impossible to actually 

 witness the fastening of the larva. But what has been observed 



