SEA-FISHERIES LABORATORY. 221 



Two to four specimens have been found after examining 

 numerous catches of young cod of one dozen each. The 

 ratio thus varies from one in three fish to one in six. In 

 one or two instances two and sometimes three specimens 

 were found on young cod eight inches long. The length 

 of a full grown female Lerncea is a little over one inch. 



The adult female is securely fastened to its host by 

 strong branched horns, three in number, which are buried 

 in the tissues of various parts of the gill arches. In 

 many instances the head was found to have actually 

 penetrated the ventral aorta. To obtain the specimens 

 in an entire condition the tissues of the host have to be 

 carefully dissected. Attempts to remove them by force 

 always result in the head being left in the fish. The 

 parasite, when once fixed, remains in the same position 

 throughout life. When it dies the softer parts decay, but 

 the head continues for a long time embedded in the tissues 

 of the host, and is often met with there when dissecting 

 out living specimens. 



External Characters. 



The adult female (Plate IV., fig. 1) is cylindrical. It 

 is unsegmented, but roughly divided into three parts — a 

 globular head with anchor-like processes, connected by a 

 narrow neck to a much swollen posterior part. 



The globular head corresponds to part of the cephalo- 

 thorax in Lepeoj^htheirus. It is furnished with three 

 more or less branched horns, two lateral and one median 

 and dorsal. The head is slightly curved downwards, ter- 

 minating in a conical apex. 



The anterior portion of the neck represents the 

 remainder of the cephalo-thorax and the fourth thoracic 

 segment. The whole of the neck is marked by fine trans- 

 verse lines. 



