SEA-FISHERIES LABORATORY. 205 



of six weeks in filtered sea water without visible food of 

 any kind. 



From the large numbers of flounders examined in the 

 Piel laboratory, partly in connection with this memoir, 

 but chiefly in connection with fisheries work, during the 

 past year or two, the conclusion has been arrived at, that 

 Lepeojyhtheirus pectoralis to some extent feeds on blood, 

 and may be hurtful to the fish, especially when present 

 in numbers (see figure on p. 6). 



The appendages are more suited for a sedentary life 

 than even a semi-pelagic one. The animals can only 

 remain swimming for short periods, and their presence in 

 tow-nettings, therefore, is accidental. They do not, under 

 normal conditions, and as long as the fish remains in a 

 healthy state, leave their host. In the fish tanks at Piel 

 over 150 flounders, all more or less infested with 

 Lejjeophtheirus, are kept during the spawning season. 

 The waste water from the tanks is carefully filtered for 

 periods of at least three months in the spring, to collect 

 the eggs shed by the fish. Yet not even one specimen of 

 the parasite has been found in the filter. When the 

 fish are examined and the parasites removed, no matter 

 how carefully, the skin, especially where there are a 

 number close together, is usually lacerated and bleeding. 

 The males and immature females on the general surface 

 of the body do not seem to remain long enough in one 

 place to cause obvious injuries. Under the fins, however, 

 and on the fins themselves, where the egg-bearing females 

 are usually found, and where they lie for weeks in the 

 same position if not disturbed, is the part of the fish 

 chiefly injured. The pectoral fin in some instances may 

 be partially destroyed, and pieces of the tissues are fre- 

 quently found enclosed in the second maxillipedes of the 

 parasite. 



