6 BRITISH COPEPODA. 



The colouring of the Copepoda varies very con- 

 siderably, as does that of many larger Crustacea, with 

 that of their food material and of the vegetation 

 amongst which they live ; a large number of the 

 oceanic species are translucent and almost colourless, 

 but one of these — Anomalocera Patersonii — often 

 exhibits wonderfully brilliant tints of blue, red, and 

 green ; Peltidium interruptum, which is also chiefly an 

 oceanic species, is constantly of a deep reddish-brown 

 colour, and almost all the flat-bodied species (Pel- 

 tidiidas, Glaus) are banded to some extent, sometimes 

 very gorgeously, with shades of red or purple ; the 

 same may be said of some few species of Harpacticidse, 

 notably of Thalestris rufocincta, Norman, T. longi- 

 mana, Claus, T. rufoviolascens, Claus, and Westwoodia 

 nobilis, Baird. The colours of most of these are given 

 as faithfully as possible in the plates illustrating the 

 various species. The usual colour of the marine 

 Copepoda, however, is a transparent yellowish brown 

 or straw colour, against which the eye shows as a 

 spot of brilliant ruby red, the internal digestive and 

 glandular organs often being apparent as patches of a 

 darker brown. The ovisacs, especially in some fresh 

 water species, not unfrequently exhibit characteristic 

 tints of blue, brown, or green ; but the colouring of 

 the inhabitants of fresh water seems to vary remark- 

 ably according to the locality and nature of food. 

 Thus, Diaptomus Castor, Jurine, is usually of some 

 shade of light brown, often with bluish ovisacs ; but 

 in an elevated Westmorland tarn I have found it of a 

 brilliant vermilion red ; and in peaty pools of no very 



