264 THE COURTSHIP OF ANIMALS 



but only to the males in their competition for the possession 

 of the females." 



Much uncertainty would seem to exist in regard to 

 two very extraordinary marine species of Copepoda. In 

 one, Calocalanus pavo the male possesses enormous 

 antennae, and a remarkable development of iridescent 

 feather-Hke structures at the end 6f the body, arranged 

 in a sort of open fan-work ; the female has what may be 

 called " normal " antennae, and a brush-Hke tuft at the 

 end of the body. In the other species — Calocalanus 

 plumulosus — of which the female only is known, there is 

 a similar arrangement of plume-like structures at the 

 end of the body, but all but one are extremely small ; 

 the single plume differs from the rest in being of enormous 

 length. Commonly these structures are regarded as 

 mechanisms to reduce the expenditure of energy 

 necessary to keep at the surface of the water, for these 

 creatures inhabit the surface-waters of the open ocean. 

 Many larval Crustacea inhabiting similar areas are in like 

 manner kept afloat, or at any rate aided in keeping afloat, 

 by the excessive development of spines. But if this be 

 the purpose of these strange excrescences of Calocalanus 

 it seems curious that the female of C. pavo should not 

 be similarly provided. If they are to be regarded as 

 secondary sexual characters it is curious that the females 

 of C. pavo and C. plumulosus should be so utterly dis- 

 similar. The male of C. plumulosus is unknown. On 

 the whole, it seems more reasonable to regard these strange 

 structures as mechanical aids to swimming rather than 

 as secondary sexual characters. 



