844 
THE VOYAGE OF H.M.S. CHALLENGER. 
ftnmarchicus, and nearly allied forms, are the most characteristic members of the surface 
fauna ; while, judging by the results of the Challenger Exjdedition, the warm equatorial 
and subtropical areas present a much greater variety of species. Undina darwinii and 
Euchceta prestcindrece may be regarded as holding the same position in the tropical and 
warm temperate seas as Calanus finmarchicus in the cold zones ; but there are several 
other species which follow close upon these. 
A, female, seen from the left side ; B, male, seen from the left side ; C, female, seen from the dorsal surface, pr, ocular 
process ; ov, ova ; sjp, spermatophores ; mxp, posterior foot-jaw ; i, intestine ; m, dorsal muscles. 
As in the case of many purely pelagic or aquatic animals, the range of distribu- 
tion of many of the marine Copepoda is extremety wide ; and one point of paramount 
interest is the relation of natatory forms of extremely wide distribution, and as an 
interesting illustration may be mentioned Zaus spinatus and Harpacticus fulvus these 
two species inhabiting precisely the same kind of places respectively in Northern 
