PODOPLEA ISOKERANDRIA 69 



Nicothoe and some of the Dichelestiidae ^ have more numerous 

 joints. In most of the Dichelestiidae, however, the number of 

 joints is less than seven and practically equal in the two sexes. 



TRIBE II. ISOKERANDEIA. 



The first antennae are short, similar in the two sexes, and 

 are never used by the 'male as clasping organs. This function 

 may be subserved by the second maxillae. 



Fams. Oncaeidae, Cokycaeidae, Lichomolgidae, Erga- 



SILIDAE, BOMOLOCHIDAE, ChONDEACANTHIDAE, PhILICHTHYIDAE, 



Nereicolidae, Heesiliidae, Caligidae, Leenaeidab, Leenae- 



OPODIDAE, ChONIOSTOMATIDAE. 



The families Oncaeidae and Corycaeidae contain pelagic forms of 

 flattened shape and great swimming powers, but the structure of the 

 mouth-parts in the Corycaeida.e points to a semi-parasitic habit. 



Fam. 1. Oncaeidae. — This family, including the genera 

 Oncaea, Pachysoma, etc., does not possess the elaborate eyes of 

 the next family, nor is the sexual dimorphism so marked. 



Fam. 2. Corycaeidae. — These are distinguished from the 

 Oncaeidae, not only by their greater beauty, but also by the 

 possession of very elaborate eyes, which are furnished with two 

 lenses, one at each end of a fairly long tube. The females of 

 Sapphirina are occasionally found in the branchial cavity of 

 Salps, and their alimentary canal never contains solid particles, 

 but is filled with a fluid substance perhaps derived by suction 

 from their prey. S. opalina may occur in large shoals, when the 

 wonderful iridescent blue colour of the males makes the water 

 sparkle as it were with a sort of diurnal phosphorescence. The 

 animal, however, despite the opinion of the older observers, is 

 not truly phosphorescent. It may be that the ornamental 

 nature of some of the males is correlated with the presence of 

 the curious visual organs, which are on the .whole better de- 

 veloped in the females than in the males. As in so many pelagic 

 Copepods, the body and limbs may bear plumed setae of great 

 elaboration and beautiful colour, e.g. Gopilia vitrea, (Fig. 3*7). 



We now pass on to the rest of the parasitic Copepods,^ which 



^ Heller, Reise dcr Novara, vol. iii., 1868. 



^ For fish -parasites in British waters consult Scott, Fishery Board for Scotland, 

 Scientific Investigations, xix., 1900 et seq. 



