35 



The remainder of the neck and the g'reater part of the 

 swollen mass behind corresponds to the genital segment. 

 The abdomen is represented by the terminal portion of 

 the swollen part, and gradually tapers to a blunt end. 

 The swollen region of the genital segment is abruptly 

 bent into the form of the letter S (Plate TV., fig. 1). 



The appendages are rudimentary, the greater number 

 being entirely absent. Those present are the first pair 

 of maxillipedes placed at the apex of the head, immediately 

 under the mouth, and four pairs of swimming feet at the 

 anterior end of the narrow neck. The swimming feet are 

 exactly as they exist in the cyclops stage both in size and 

 structure. The protopodite is two-jointed, the exopodite 

 of the four pairs is two-jointed. The endopodite of the 

 first two pairs is also two-jointed. The third and fourth 

 pairs of feet have no endopodite. 



The external openings are, the mouth placed at the 

 apex of the head, the openings of the oviducts situated 

 on the ventral aspect of the S-shaped region, and the anus 

 at the blunt apex of the abdomen (Plate IV., fig. 1, an.). 



The colour of the living animal is dark red, due to the 

 contained blood. When removed from the fish and placed 

 in sea water the colour changes to white. Lerna'a does 

 not live long after being taken from the fish. The 

 longest period observed was about twelve hours. They 

 are simply inert sacs quite incapable of movement. 

 Occasionally the parasites are covered with colonies of 

 hydroids which sometimes entirely obscure them. The 

 exoskeleton consists of a chitinous cuticle moderately thin 

 and soft in the region of the swollen part, but thick and 

 hard on the neck and head. 



Immature Lerncea hrcmchialis living on the apex of the 

 gill filaments of the flounder (Plate IV., figs. 3, 4, and 5) 

 are cyclopoid in appearance. The animal is oval in trans- 



