192 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



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, C aligns 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 Caligus, 

 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 (Midler). 



This species was first described by 0. F. Mtiller* under 

 the name Lerncea pectoralis. 



Mode of Occurrence. 



Lepeophtheirus j^ectoralis is most frequently found upon 

 the "white fluke" or flounder (Pleuronectes flesus). It 

 also occurs on the plaice, dab, sole, &c. 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 

 * Prodroni. Zoolog. Dan., 177G. 



