Ko. 640] PARASITIC COPEFODS 



451 



swim about with a snappy spiral dart. They may thus 

 swim about for nearly two days, constantly searching for 

 a host to wliicli to attach themselves. They dart here, 

 there and evcrx wli('r(' : if not successful in meeting a host, 

 they soon die l)iit it' one is found they attach themselves 

 and carry on tlicir life-cycles to completion. 



In Sahiiiinnfd rrhnirrlsii it has been found that the 

 larval coi)ci>()(l> >\\ im about near the surface of the water 

 throughoiil llic (lay, at night they sink down to lower 

 depths near the bottom of the stream. These migrations, 

 although contrary to the general migrations of free-living 

 copepods, are, nevertheless, of great benefit to these para- 

 sitic forms in that they are parallel with the migrations 

 of the hosts. Brook trout generally feed near the upper 

 surfaces of the streams during the day and at night they 

 sink down to lower levels. This similar behavior on the 

 part of the parasite and the host makes it much easier 

 for the parasite to meet its host and thereby carry out 

 its life-cycle. 



The manner in wliich the larval copepod attaches itself 

 to the host is extremely interesting. Each larva posses- 

 ses powerful mouth parts and a peculiar attachment fila- 

 ment which aid in the attachment of the organism. On 

 coming in contact with a desirable portion of the host, 

 the parasite first rasps a lioli^ in the tissues by means 

 of its mouth parts. Then tlic attachment filament is 

 brought in contact with thi- cavity and by means of the 

 contraction of numerous thin head muscles which are 

 attaclicd to the i>roximal end of the attachment filament, 

 the hnlb-like distal end of the filament is driven into the 

 cavity. The ulne-like secretion of the attachment fila- 

 ment' as well as the reueneratiiig tis>ne of the ho^t >oon 

 attach the copepod (,nitc securely. 



segmentation as well a- its ])lu)nose swinmiing feet. The 

 abdomen round- ont, becomes larger and more bag-like 

 in outline. The month parts also change their appear- 

 ance. The mouth itself grows into a prominent tube-like 



