572 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvm. 



prehensile apparatus which holds the Caligus securely to its host, even 

 in the presence of so much friction. 



Of course the color of the Caligus harmonizes better with the pig- 

 mented side of the fish; on the under surface the copepod stands out 

 in strong contrast with its surroundings. 



The Qgg strings in this species are comparatively short, and this gives 

 the female greater freedom of motion. Both males and females are 

 more lively than most species, and they manifest this activity fre- 

 quently by leaving their host and swimming about freely. This hap- 

 pens more often at night than during the daytime, and several investi- 

 gators have recorded the capture of both sexes in the tow along with 

 free forms. 



Such a habit possibly helps in explaining their presence upon so 

 many different kinds of fish. Many of the latter, no doubt, are mere 

 temporary makeshifts to tide over a necessary interval and to keep 

 the copepod supplied with food until it can return to its regular host. 



Associated with its distribution among so many hosts is a consider- 

 able variation in the color pattern. Most specimens have a pale 

 orange tint and are more or less transparent, but it can be readily 

 seen that those obtained from dark fish or from the darker pigmented 

 surface are themselves of a deeper color and more opaque than others 

 from light fish or from a nonpigmented surface. The difference is due 

 to an increase or decrease in the number of pigment spots and not to 

 any fundamental change in the pigment itself. Each spot consists of 

 an uniformly colored center as if washed in with water color, and 

 long irregularly radiating filaments. The spots are thickest along the 

 margin of the carapace where the filaments are interwoven into a dense, 

 narrow band, close to the margin. Similar but much wider bands are 

 found along the sides of the genital segment and the abdomen. There 

 is also a spot of pigment just dorsal to the furca, and another upon 

 either side on the basal lamina of the third pair of legs, showing dor- 

 sally between the carapace and abdomen. The frontal plates, the 

 region over the e} T es, the whole of the thorax, including the segments 

 fused with the head, and the center of the genital segment and abdo- 

 men are ordinarily free from pigment. 



This species has been secured from the following fish on the North 

 American coast, mostly by the United States Bureau of Fisheries. The 

 numbers are those given to the separate lots in the National Museum. 

 From the common flounder {Pseudopleuronectes americanus), lots 1267 

 and W. 18; from the four-spotted flounder {Paralichthys oblongtis), lot 

 12607; from the cod (Gadus morhua), lots 8112, 8115, 12635, 12636, 

 12638, 12640, 12641, 12662, 19893; of those collected and numbered by 

 Vinal N. Edwards, V. N. E. 1405, 1412, 1413, 1417, 1420, 1423, 1462, 

 1466; of those collected and numbered by the author, W. 8, 10, 16, 22; 

 from the haddock (Melanogrammus aeglefinus), lots 12611, 12626, 12640, 



