236 RESEARCH SEMINAR. 



July 22. Habits and Life-History of Parasitic Copepods. 



By CHARLES B. WILSON. 



A statement was first made of some of the problems confront- 

 ing the student of this group, for only one of which has there 

 been any attempt at solution. This is the one which logically 

 comes first, the determination and description of species. But 

 it is the least important and should be quickly followed by a 

 careful study of habits, including relative abundance and the 

 influence of the parasite upon its host. The life-history must 

 also be worked out before adequate methods can be devised for 

 exterminating the parasites or checking their ravages. Then 

 come a series of ecological problems for which these copepods 

 afford exceptionally fine material, color protection, mimicry, 

 adaptation to environment, degeneration phenomena, and the like. 



Material was shown for several of these problems, with a series 

 of drawings for the life-history of the Caligidae, the largest family 

 in the group. The history of three members of this family, 

 Caligus rapa.r, Caligus bonito and Alebion glabritin, was presented 

 in full, that of others only partially. 



The eggs hatch into a typical nauplius which swims about 

 freely at the surface. After the second or third moult it becomes 

 a metanauplius whose second antennae cease to function as loco- 

 motor and become prehensile. At this stage it seeks its host 

 and fastens to it. 



In Caligus, Lepcophtheirus and allied genera an attachment 

 filament is developed at the next moult from a median frontal 

 gland which holds the larva securely to its host until it has 

 matured. In Alebion and allied genera the second antennae con- 

 tinue to serve as organs of attachment up to maturity. In the 

 metanauplius there are but two pairs of thoracic appendages ; a 

 pair is added at each successive moult up to the normal number. 



These parasites do not usually injure their host, but may 

 become sufficiently numerous to cause serious damage, especially 

 if the host has been weakened or injured. 



They feed upon the blood of their host which they obtain by 

 piercing the skin in the vicinity of blood vessels and extracting 

 the blood by means of a suctorial mouth tube. 



They often become a serious nuisance to the artificial breeder 



