67 
egg, and the adult condition are practically the same in 
the two genera, and probably also in the other members 
of this family. From investigations carried on during 
the past two years, it may reasonably be concluded that 
Lepeophtheirus, throughout the remainder of its life and 
under normal conditions remains on the same fish that it 
attached itself to at the beginning of the “ chalimus ” 
stage. It is very rarely met with in tow-net collections. 
On the other hand, Caligus does not always remain on the 
same fish. At the completion of its ‘chalimus”’ stage it 
frequently leaves its host, and for a time leads a pelagic 
life. Tow-net collections often contain immature males 
and females, and occasionally mature males of Calzgus, 
especially of Caligus rapax. Amongst these some may be 
found with a large notch in the middle of the frontal 
margin. This is due to the breaking of the chitinous 
filament by which they were secured to their host. The 
metamorphosis is a progressive one. 
I.—LEPEOPHTHEIRUS (Miller). 
This species was first described by O. I’. Miiller* under 
the name Lernwa pectoralis. 
MoprE or OccURRENCE. 
Lepeophtheirus pectoralis is most frequently found upon 
the ‘“‘white fluke” or flounder (Pleuronectes flesus). It 
also occurs on the plaice, dab, sole, &e. It does not con- 
fine itself to any particular part of the exterior. Males and 
immature forms of both sexes are to be found all over the 
skin on each side of the fish. Mature egg-bearing 
females, however, are usually found under the pectoral, 
the pelvic, the ventral and the dorsal fins. With careful 
* Prodrom. Zoolog. Dan., 1776. 
